Israel said it launched airstrikes against Iranian missile launchers and a nuclear research site Tuesday, and Iran struck back against Israel and across the Gulf region, targeting U.S. embassies and disrupting energy supplies and travel.

Four days into a war that President Donald Trump suggested would last several weeks or perhaps longer, nearly 800 people have been killed in Iran, including some Trump said he had considered as possible future leaders of the country.

Explosions rang out Tuesday in Tehran and in Lebanon, where Israel said it retaliated against Hezbollah militants. The American embassy in Saudi Arabia and the U.S. consulate in the United Arab Emirates came under drone attacks. Iran has fired dozens of ballistic missiles at Israel, though most of the incoming fire has been intercepted. Eleven people in Israel have been killed since the conflict began.

In other developments, the Pentagon identified four U.S. Army Reserve soldiers killed in a drone strike Sunday at a command center in Kuwait. The strike also killed two other service members.

The spiraling nature of the war raised questions about when and how it would end.

The administration has offered various objectives, including destroying Iran’s missile capabilities, wiping out its navy, preventing it from obtaining a nuclear weapon and ensuring it cannot continue to support allied armed groups.

While the initial U.S.-Israeli strikes killed Iranian Supreme Leader Ayatollah Ali Khamenei and Trump urged Iranians to overthrow their government, senior administration officials have since said regime change was not the goal.

Trump on Tuesday seemed to downplay the chances of the war ending Iran’s theocratic rule, saying that “someone from within” the Iranian regime might be the best choice to take power once the U.S.-Israel campaign is finished.

Speaking Tuesday from the Oval Office, Trump said Reza Pahlavi, the exiled son of Iran’s toppled shah, is not someone that his administration has considered in depth to take over.

As far as possible leaders inside Iran, “the people we had in mind are dead,” Trump said.

“I guess the worst case would be do this, and then somebody takes over who’s as bad as the previous person, right? That could happen,” Trump said. “We don’t want that to happen.”

Iran’s leaders are scrambling to replace Khamenei, who ruled the country for 37 years. It’s only the second time since the 1979 Islamic Revolution that a new supreme leader is being chosen. Potential candidates range from hard-liners committed to confrontation with the West to reformists who seek diplomatic engagement.

Information coming out of Iran has been limited because of poor communications, round-the-clock airstrikes and tight restrictions on journalists. But explosions rang out across Iran’s capital.

The Israeli military said it conducted a wave of airstrikes on Iranian sites that produce and store ballistic missiles. It also said it destroyed what it called Iran’s secret, underground nuclear headquarters. Without providing evidence, it said the site was used for research “to develop a key component for nuclear weapons.”

“The regime attempted to rebuild its efforts and conceal them, thinking we wouldn’t notice. They were mistaken,” said Israeli military spokesman Brig. Gen. Effie Defrin.

There was no immediate public comment from the U.S. or Iran about the site Israel named.

Iran has said it has not enriched uranium since June, though it has maintained its right to do so and says its nuclear program is peaceful.

The U.S.-Israeli strikes have killed at least 787 people in Iran, according to the Red Crescent Society. In Lebanon, where Israel launched retaliatory strikes on the Iranian-supported militant group Hezbollah, 50 people were killed, including seven children, Lebanon’s health ministry said.

Kuwait, which had previously reported a single death, said Wednesday that an 11-year-old girl was killed by falling shrapnel as Kuwaiti forces were intercepting “hostile aerial targets.” In addition, three people were killed in the United Arab Emirates and one in Bahrain.

The U.S. military has confirmed six deaths of American service members.