A series of attacks between the US and Iran over the past several days led President Donald Trump to declare the end of a ceasefire meant to halt the fighting that the US and Israel began on February 28, though Trump has left the door open to continued negotiations.
Iran said it closed the vital Strait of Hormuz after firing a warning shot that struck a vessel travelling on an unapproved route. It warned that any retaliation over the incident would be met with a "severe response".
US Central Command identified the vessel as the M/V GFS Galaxy, a Cyprus-flagged container ship, saying it suffered significant engine-room damage and that a civilian crew member was missing.
The war has destabilised the Gulf, while Iran's effective blockade of the Strait of Hormuz has caused energy prices to surge, fuelling global inflation. Higher prices, especially for gasoline, are a politically sensitive issue for Trump ahead of November congressional elections.
Iran said several ships attempted to move through the waterway on an "unauthorised route" and disregarded warnings to correct their course.
The strait - which was a conduit before the war for one-fifth of the world's oil and LNG supplies - will remain closed until "the end of US interference in this region", the Revolutionary Guards said.
Central Command said it began its strikes at 7:15pm on Saturday (9:15 Sunday AEST), roughly an hour after the Iranians released their statement, which included a warning that "new enemy bases" in the Middle East would be targeted if the United States retaliated for the container ship incident.
Trump ordered the strikes, Central Command said. The White House did not immediately respond to a request for comment.
Washington demands that Tehran publicly state it will stop attacks on ships in the strait - and that all lanes will be open without tolls, senior US officials have said.
Iran's Foreign Minister Abbas Araqchi has accused the United States of violating the ceasefire agreement.
"There can only be mutual compliance," he wrote on X on Friday.
The US revoked the licence authorising the sale of Iranian crude on Tuesday after three Qatari and Saudi commercial tankers came under fire earlier in the week, prompting the US to hit Iranian sites. Iran then struck US military sites in Gulf states.
While Iran has not claimed responsibility for the ship attacks, analysts say Tehran uses such actions to gain leverage in negotiations.
A senior Iranian source told Reuters that Iran, the US, Qatar and Pakistan had agreed to negotiate in a call that mediators were trying to arrange for Saturday while Araqchi was in Oman, a Gulf state trying to mediate an end to the war.
Araqchi and Omani Foreign Minister Badr Albusaidi met in Oman to exchange "views on appropriate mechanisms for the safe passage of ships through the Strait of Hormuz," according to a statement from the Iranian foreign minister.
Oman's state news agency said Omani and Iranian negotiators would continue talks "at the technical and political levels".
CNN reported on Saturday that Oman made a draft proposal for the strait, including free navigation through its southern corridor in Omani territorial waters.
The plan called for vessels transiting the northern corridor through Iranian territorial waters to obtain prior approval from Iran, although no tolls would be imposed, CNN saidThe White House and State Department did not immediately respond to requests for comment on the CNN report.
A written statement from Iran's new supreme leader, Ayatollah Mojtaba Khamenei, on Saturday threatened vengeance for the death of his predecessor and father, who was killed in the war's initial attacks. It said the vengeance would take place whatever happened to Iran.
"We pledge to avenge the blood of the martyred leader and all the martyrs," the message said.
The statement was released to mark funeral ceremonies for the former leader, Ayatollah Ali Khamenei, on Thursday. His son did not attend the ceremony and has not been seen in public since the war began.
Trump had posted on Friday that he had ordered the US military to be prepared to launch thousands of missiles against Iran if Tehran attempted to assassinate him.
The Wall Street Journal and other US media reported in recent days that Israel had shared intelligence with Washington that Iran had recently devised a plan to assassinate Trump.
Iran has not commented on the assassination claims.
At the funeral ceremonies on Thursday, a huge crowd of mourners packed a courtyard, some bearing banners reading, "We Will Kill Trump".
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