Israel launched new air strikes targeting Tehran and expanded its military campaign to include attacks on Iran-backed Hezbollah militants in Lebanon on Monday, as U.S. President Donald Trump signaled the U.S.-Israeli military assault on Iranian targets could continue for weeks, Reuters reported.

Israel said it was attacking sites connected to Lebanon’s Shi’ite Muslim armed group Hezbollah, one of Tehran’s principal allies in the Middle East, after Hezbollah acknowledged launching missiles and drones toward Israel in retaliation for the killing of Iran’s Supreme Leader Ali Khamenei.

The Israeli military said it intercepted a projectile launched from Lebanon, while others landed in open areas of the country.

Israel carried out air strikes on the Hezbollah-controlled southern suburbs of Beirut on Monday, with more than a dozen explosions rocking the Lebanese capital. Israel said it also struck senior Hezbollah militants near Beirut.

People fled on foot and by car in Beirut, clogging the roads, after the series of strikes began around 2:40 a.m. (0040 GMT).

Israel and Lebanon had agreed to a U.S.-brokered ceasefire in 2024 after more than a year of fighting that left Hezbollah severely weakened.

The Hezbollah and Israel tit-for-tat attacks widen the conflict that has spread through the Middle East since the United States and Israel attacked Iran on Saturday, sending oil prices soaring and snarling air travel.

Lebanon’s presidency said on Saturday it had been told by the U.S. ambassador that Israel would not escalate against Lebanon as long as there are no hostile acts from the Lebanese side.

The Israeli military said Hezbollah was “fully responsible for any escalation” and warned residents of dozens of villages in southern and eastern Lebanon to evacuate.

The Israeli military said late on Sunday that its air force had established aerial superiority over Tehran, and that a wave of strikes across the capital had targeted intelligence, security, and military command centers, read the report.

In Iran, President Masoud Pezeshkian said a leadership council composed of himself, the judiciary head and a member of the powerful Guardian Council had temporarily assumed the duties of Supreme Leader.

Air raid sirens sounded across Israel late on Sunday, including in Tel Aviv where projectiles were seen streaking across the night sky as Iran fired new barrages of missiles.

The first U.S. casualties of the campaign, including the deaths of three service personnel were confirmed on Sunday. Two U.S. officials, speaking on condition of anonymity, told Reuters the U.S. service members were killed on a base in Kuwait.

Trump paid tribute to the three killed as “true American patriots” but warned that there will likely be more casualties. “That’s the way it is,” he said.

An extended military campaign could pose a major political risk for Trump’s Republican party ahead of U.S. midterm elections that could decide the fate of Congress. Only around one in four Americans approve of the operation, according to a Reuters/Ipsos poll on Sunday.

But in a video posted on Sunday, Trump vowed military strikes on Iran will continue until “all our objectives are achieved” without providing specifics. He said the assault had so far wiped out Iran’s military command and destroyed nine Iranian navy ships and a naval building.

American aircraft and warships have struck more than 1,000 Iranian targets since the start of major combat operations on Saturday, the U.S. military said.

Trump called on Iran’s military and police, including the powerful Islamic Revolutionary Guards Corps (IRGC), to stop fighting, promising immunity for those who surrender and threatening “certain death” for those who resist. He reiterated calls for the Iranian people to revolt against the government.

“I call upon all Iranian patriots who yearn for freedom to seize this moment, to be brave, be bold, be heroic and take back your country,” Trump said in the pre-recorded video. “America is with you.”

In interviews with multiple news outlets, Trump said the military campaign against Iran could continue for at least four weeks. Top Trump administration officials were set to brief the full membership of the U.S. Senate and House of Representatives on Tuesday, a White House spokesperson said.

Following the death of Khamenei, Iran faces a power vacuum that could leave it in chaos, but the Trump administration has not outlined longer-term aims for the country.

Departing from what had become his usual practice while staying at his Mar-a-Lago resort in Florida, Trump did not speak with the pool of reporters that travel with him. No administration officials appeared on Sunday political talk shows in the U.S.

The Trump administration wants to avoid sending mixed signals as officials continue to debate policy details internally, a person familiar with the discussions told Reuters.

Iran’s Revolutionary Guards said on Sunday they had hit three U.S. and UK oil tankers in the Gulf and the Strait of Hormuz, and attacked military bases in Kuwait and Bahrain with drones and missiles. Shipping data showed hundreds of vessels including oil and gas tankers dropping anchor in nearby waters with traders expecting sharp jumps in crude oil prices on Monday, Reuters reported.

Global air travel was also heavily disrupted as continued air strikes kept major Middle Eastern airports closed, including Dubai — the world’s busiest international hub — in one of the biggest aviation interruptions in recent years.

Oman’s foreign ministry said Iranian Foreign Minister Abbas Araqchi had indicated Tehran was open to de-escalation. But in a post on X, Araqchi suggested Iran was ready to keep fighting.

It remained unclear what the longer-term prospects were for Iran to rebuild its leadership and replace 86-year-old Khamenei, who had held power since the death of the founder of the Islamic Republic, Ayatollah Ruhollah Khomeini in 1989.

Experts said that while his death and those of other Iranian leaders would deal Iran a major blow, it would not necessarily spell the end of Iran’s entrenched clerical rule or the sway of the elite Revolutionary Guards over the population.

Still, it was too early to say how the Iranian people would respond to the changes. A new analysis of Iranian social media from Redpoint Advisors, a global intelligence firm, suggests the public is already looking beyond Khamenei for his replacement.