Here’s a look at the first four days of attacks between Israel and Iran.

Iranian officials have long asserted that their country’s nuclear program is intended solely for peaceful purposes, such as energy production and scientific research. But revelations in the early 2000s about undisclosed nuclear facilities, and work done up until 2003 on the design and delivery of nuclear weapons, led many nations to conclude that the country was walking to the threshold of becoming a nuclear weapons state.

Iran operates more than 30 facilities around the country that carry out different steps of the nuclear fuel cycle, including uranium enrichment, according to the Nuclear Threat Initiative. Tehran insists that its enrichment program is meant only to produce fuel for nuclear reactors.

Uranium enriched at low levels can be used as fuel for civilian purposes. Highly enriched uranium is used to make nuclear bombs, and Iran’s enrichment facilities (at Natanz and Fordo) contain advanced centrifuges capable of enriching uranium to high levels.

More than a dozen other facilities produce, test or house missiles, or otherwise support Iran’s missile program.

In 2015, President Barack Obama negotiated an agreement to limit Iran’s nuclear ability and to require monitoring and reporting requirements in return for lifting international oil and financial sanctions.

President Trump withdrew from the deal in 2018, saying it was not tough enough.

Late last month, the United States presented its first formal proposal to Tehran for elements of a new nuclear deal. The U.S. offer came hours after United Nations inspectors reported a major surge over the previous three months in the size of Iran’s stockpile of near-bomb-grade uranium. It proposed permitting Iran to continue to enrich uranium at low levels until an international consortium began manufacturing fuel for customers around the Middle East. President Trump said Iran appeared to have rejected the plan to ultimately stop it from enriching uranium on Iranian soil.

David E. Sanger contributed reporting.

After Israel launched a surprise assault on Iran on Friday, confrontation between the two countries has escalated over four days, with neither side showing signs of heeding international calls for restraint. Here is a recounting, with maps, videos and photos, of the major developments in the first few days of the conflict.

Friday, June 13

In the early hours of Friday, Israel launched several waves of strikes at Iran, attacking military targets including nuclear sites and top commanders. The strikes prompted a retaliatory barrage of missiles from Iran, which struck at least seven sites around Tel Aviv.

Iran reported on Friday that 78 people had been killed and hundreds injured. Among the dead were two high-ranking military officers, Maj. Gen. Mohammad Bagheri and Gen. Hossein Salam, and senior nuclear scientists.

Israel attacked Iran’s premier nuclear enrichment site at Natanz, about 140 miles south of Tehran, destroying the site’s aboveground plant and main electricity infrastructure.

In the early afternoon, Israel carried out a strike on a military airport in the northwest Iranian city of Tabriz. A witness video verified by The New York Times shows large plumes of black smoke rising into the sky from the airport.

A section of a multistory residential building near Nobonyad Square, in northeastern Tehran, collapsed after it was struck, according to videos of the immediate aftermath that were verified by The Times.

Iran’s retaliatory strikes hit the Kirya area in central Tel Aviv, which is home to a number of government and military facilities, including the headquarters of the Israel Defense Forces. Several buildings in the area were damaged.

Saturday, June 14

Overnight, the Israeli military struck sections of Mehrabad International Airport in Tehran, and videos verified by The Times show thick black smoke billowing from the airport’s military hangars.

An Iranian missile landed in a residential area of Rishon LeZion, south of Tel Aviv. A video taken later shows extensive damage to homes there.

On Saturday evening, Israel intensified its attack on critical energy infrastructure in Iran, widening its military campaign. Drones targeted a section of the South Pars Gas Field in Bushehr Province, one of the world’s largest gas fields and a critical part of Iran’s energy production.

Later, Israel took out two major energy facilities in Tehran: the Shahran fuel and gasoline depot and Shahr Rey, one of the country’s largest oil refineries. A video verified by The Times shows the Shahran depot ablaze.

Sunday, June 15

Iranian missile barrages on Israel killed at least eight people overnight, including four in the city of Bat Yam, south of Tel Aviv, where a blast heavily damaged a multistory apartment complex.

Israel bombarded Tehran in a rare daytime assault on Sunday afternoon.

Israel said it had also struck an airport in Mashhad.

Iran’s health ministry reported that at least 224 people had been killed and more than 1,400 injured. Israel’s death toll was at least 24, with roughly 600 injured, according to the Israeli government.

Monday, June 16

Early Monday morning, the Israeli military warned residents in several areas of an imminent Iranian attack and urged them to remain near shelters and safe rooms. Iran struck a residential block in Petach Tikva, in central Israel, killing at least four people, officials said.

Iranian missiles also hit Israel’s largest oil refinery, located in Haifa Bay in northern Israel, according to footage verified by The Times.

The Israeli military claimed it had attacked the elite Quds Force’s command center in Tehran, though the claims could not be verified independently.

The Israeli military later published an announcement on social media telling people in a densely populated residential district of northeastern Tehran to evacuate, saying it planned to target military infrastructure there.

Hours later, Israel stuck the offices of Iran’s state broadcaster, the Islamic Republic of Iran Broadcasting, which is in the same district. Video feeds, verified by The Times, show the headquarters of the broadcaster burning and thick pillars of smoke rising from the building.

News Analysis

Iran’s most heavily fortified nuclear site, Fordo, was built deep inside a mountain to protect it from an attack. Only the U.S. military has the 30,000-pound bomb capable of even reaching it.

The bomb is commonly known as a “bunker buster” because it is designed to destroy deep underground bunkers, or well-buried weapons in highly protected facilities. It is believed to be the only air-delivered weapon that would have a chance of destroying the site.

The bomb has a much thicker steel case and contains a smaller amount of explosives than similarly sized general-purpose bombs. The heavy casings allow the munition to stay intact as it punches through soil, rock or concrete before detonating.

Its size — 20 feet long and 30,000 pounds — means that only the American B-2 stealth bomber can carry it.

Conventional wisdom has been that Israel can’t destroy Fordo on its own. The United States has blocked Israel from getting the bunker buster, and while Israel has fighter jets, it has not developed heavy bombers capable of carrying the weapon.

But Israel can come close by hitting more accessible power generation and transmission plants that help run the facility, which contains Iran’s most advanced centrifuges, military officials said.

In conjunction with Israel’s aerial bombardment of Iran, going after the Fordo-adjacent plants could significantly slow down the ability of Iran’s most protected nuclear facility to keep enriching uranium.

The Israel Defense Forces and covert operatives could also look for other ways to disable the site, including destroying the entrance to it.

Attacking Fordo is central to any effort to destroy Iran’s ability to make nuclear weapons. In March 2023, the International Atomic Energy Agency reported that it had discovered uranium that had been enriched to 83.7 percent purity in Fordo — close to the enrichment level, 90 percent, necessary for nuclear weapons.

Iran, which is a signatory to the Nuclear Nonproliferation Treaty, has maintained that its nuclear program is for peaceful purposes.

The U.S. Air Force is moving refueling tankers, aircraft and additional warplanes to support any additional American operations in the Middle East, U.S. officials said.

But President Trump has not, at the moment, moved to reverse years of American policy on providing Israel with the bunker buster bombs.

“We’ve had a policy for a long time of not providing those to the Israelis because we didn’t want them to use them,” said Gen. Joseph Votel, who was commander of U.S. Central Command during Mr. Trump’s first term. Instead, the United States viewed its bunker buster bomb largely as a deterrent, a national security asset possessed only by America, but not one that, if made available, might encourage Israel to start a war with Iran.

Iran built the centrifuge facility at Fordo knowing that it needed to bury it deep to prevent it from being attacked. In 1981, using F-15 and F-16 fighter jets, Israel bombed a nuclear facility near Baghdad as part of its effort to stop Iraq from acquiring nuclear weapons. That facility was above ground.

“The Iranians fully understood that the Israelis would try to get inside their programs and they built Fordo inside of a mountain a long time ago to take care of the post-Iraq problem” presented by the 1981 strike, said Vali Nasr, an Iran expert who is a professor at Johns Hopkins University.

Over the years, the Israelis have cooked up a variety of plans to attack Fordo in the absence of U.S.-supplied bunker busters. Under one of those plans, which they presented to senior officials in the Obama administration, Israeli helicopters loaded with commandos would fly to the site. The commandos would then fight their way inside the facility, rig it with explosives and blow it up, former U.S. officials said.

Israel successfully mounted a similar operation in Syria last year when it destroyed a Hezbollah missile production facility.

But Fordo would be a much more dangerous endeavor, military officials said.

American officials say now that Israel has gained air supremacy over much of Iran, Israeli attack planes could circle over Fordo and render it inoperable, at least temporarily, but not destroy it.

“The Israelis have sprung a lot of clandestine operations lately, but the physics of the problem remain the same,” said Gen. Kenneth F. McKenzie Jr., who was in charge of the Iran war plans when he ran the Pentagon’s Central Command after General Votel. “It remains a very difficult target.”

David A. Deptula, a retired three-star Air Force general who planned the American air campaigns in Afghanistan in 2001 and in the 1991 Persian Gulf War, agreed that Israel has options that would not require American help.

For example, Israeli special forces “could insert/apply or otherwise use a variety of means to disable the facility,” he said.

Yechiel Leiter, Israel’s ambassador to the United States, hinted at those options on Sunday on ABC News’s “This Week.”

“We have a number of contingencies, which will enable us to deal with Fordo,” he said. “Not everything is a matter of taking to the skies and bombing from afar.”

Even if Mr. Trump were to authorize American B-2 stealth bombers to drop the 30,000-pound bombs, General McKenzie said, there would be several technical, highly classified challenges in coordinating such a strike with Israel.

A decision to use the American bunker busters would also have huge international consequences, General Votel said. For one, there could be nuclear contamination from such a bombardment that could endanger civilians.

“I think there would also certainly be fallout internationally over the idea that the United States joined Israel in what would be viewed as an illegal attack on the sovereignty of Iran,” General Votel added.

And Iran could widen its retaliation to U.S. troops and other American targets in the region and beyond, military analysts say. The United States would be back on war footing in the region.

Mr. Trump has made clear that he has little interest in more military misadventures in the region, and he is seeking not to alienate a noninterventionist wing of supporters firmly opposed to more U.S. involvement in a Middle East war.

Adam Entous contributed reporting.