The Israeli military said it has launched a wave of strikes on the Iranian capital Tehran.
"The IDF (army) has...begun a large-scale wave of strikes against infrastructure of the Iranian terror regime across Tehran," a military statement said.
Israel also struck targets in Lebanon and said it intercepted missiles from Iran.
An air strike in the pre-dawn hours struck a Beirut suburb stronghold of Hezbollah, the Iran-backed force that has vowed to avenge the death of Iran's supreme leader, Ayatollah Ali Khamenei.
Israel, which had warned residents beforehand to evacuate, also said it was working to intercept a new barrage of missiles fired by Iran.
Iran has vowed to exert a heavy price for the attacks and has fired missiles across the region, and its Revolutionary Guards claimed yesterday to have closed the Strait of Hormuz, the chokepoint into the Gulf through which a fifth of the world's crude oil flows.
"The Americans' mischief and deceit could lead to the collapse of the entire military and economic infrastructure of the region," the Iranian military command warned in a statement.
Oil tanker transits through the strait have plunged by 90%, energy market intelligence firm Kpler said.
Britain's maritime agency reported a large early-morning explosion near Kuwait, with oil spilling into Gulf waters.
Nearby Iraq was hit by a total electricity blackout though it was not clear if it was connected to the war, with the electricity ministry blaming a sudden drop in gas supplies to a key plant.
Iran struck yesterday in northern Iraq's autonomous Kurdish area, killing a member from an exiled Iranian Kurdish group, a representative said.
Iranian warship torpedoed
The United States said that one of its submarines sank an Iranian warship off the coast of Sri Lanka yesterday, the nation's first torpedoing of a vessel since World War II.
The IRIS Dena frigate had been on a friendly visit to India when it was hit.
The ship "thought it was safe in international waters", US Defense Secretary Pete Hegseth told reporters.
Mr Hegseth, who has previously boasted that the war would not be "politically correct", called the strike "quiet death" and said of the United States, "We are fighting to win".
Watch: US Department of Defense video purports to show the sinking of an Iranian warship
At least 87 people were killed in the strike, Sri Lankan officials said, with 61 remaining missing. The island nation rescued 32 sailors, many of them wounded, Foreign Minister Vijitha Herath said.
Iran's official IRNA news agency said 1,045 military personnel and civilians had been killed since the war began on Saturday, a toll that has not been independently verified.
Iran says more than 150 people, many of them children, died in a strike on a school on Saturday in the southern town of Minab, with state television showing a large crowd of mourners over bodies in white shrouds.
US authorities say six soldiers have died in the war.
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Missile over Turkey
In another first, a missile launched from Iran was destroyed by a NATO air defence system while heading towards Turkey's airspace, drawing condemnation from Ankara and NATO.
A Turkish official said that Turkey was not the target of the missile, which had been aimed at a British base in Cyprus and "veered off course".
Turkey, which has criticised the war, summoned the Iranian ambassador, and its Foreign Minister Hakan Fidan told his Iranian counterpart Abbas Araghchi in a telephone call that "any steps that could lead to the spread of conflict should be avoided".
The UAE, Saudi Arabia and Qatar all said they had intercepted Iranian missiles yesterday, including a drone which appeared aimed at Saudi Arabia's huge Ras Tanura refinery.
Kuwait has also been struck, with the health ministry announcing the death of an 11-year-old girl after she was hit by falling shrapnel.
Thirteen people, seven of them civilians, have been killed in countries around the Gulf since the war began, and air travel has been severely disrupted.
The United States said it sent its first charter flight to bring back Americans after urging them to leave the region, following similar moves by France and Britain.
Warning on Lebanon
In Lebanon, Israeli strikes have killed 75 people and displaced more than 83,000 since the start of the new round of fighting, officials said yesterday.
Israel urged people to leave the section of Lebanon south of the Litani river, an area of hundreds of square kilometres, as the army was "compelled to take military action".
Israeli air strikes also hit a hotel in Hazmieh yesterday, the first reported attack on the predominantly Christian area in Beirut's suburbs, which is near the presidential palace and several foreign embassies.
The strikes revived memories of previous long-term Israeli occupations in Lebanon, and AFP video footage showed what appeared to be two Israeli tanks amid residential buildings in Khiam, about 6km into Lebanon.
French President Emmanuel Macron, in a telephone call with Israeli Prime Minister Benjamin Netanyahu, warned Israel against a ground offensive and to "preserve Lebanon's territorial integrity",
It was mR Macron's first conversation since last year with mR Netanyahu, who had voiced anger over France's historic recognition of a Palestinian state.
The French leader also said he spoke to Lebanese leaders to urge them to press Hezbollah to cease its attacks.
Iran's military threatened to target Israeli embassies worldwide if Israel were to attack Tehran's mission in Lebanon.
