The United States early Wednesday reimposed a blockade on Iranian ports following Tehran's attacks on vessels transiting the Strait of Hormuz, triggering fresh missile strikes on countries hosting US forces as an interim peace agreement continued to unravel.
Days of retaliatory attacks between Iran and the United States, coupled with both sides' efforts to assert control over the strategic waterway through which around one-fifth of the world's oil and natural gas passes during peacetime, have fuelled fears of a return to full-scale conflict in the Middle East.
Washington first imposed the blockade in mid-April before lifting it in mid-June, a day after signing an interim agreement that provided a 60-day window for negotiations on issues including Iran's nuclear programme. Those talks have since stalled as fighting around the Strait of Hormuz has intensified.
When US President Donald Trump announced the blockade's reinstatement on Monday, he also proposed a 20% fee on ships using the strait. Hours later, however, he abandoned the idea, saying Gulf allies had urged a different approach.
Ahead of reimposing the blockade, the US military launched another wave of strikes, according to US Central Command.
Missile alerts were issued in Bahrain and Kuwait early Wednesday after Iranian missiles targeted the two countries, continuing a pattern of daily attacks that has further strained the fragile truce.
Hours after the blockade took effect, Iranian state media reported an exchange of fire in the Strait of Hormuz but gave no further details.
Adm. Brad Cooper, commander of US Central Command, said Iran had launched dozens of missiles and drones at neighbouring Gulf Arab states.
"US forces are holding Iran accountable for unwarranted aggression that continues to endanger innocent lives," Cooper said.
The United States currently has at least 19 warships in the Arabian Sea, including two aircraft carriers and an amphibious assault ship carrying more than 1,000 Marines. Central Command also said hundreds of military aircraft are operating across the Middle East.
Since the war involving the US, Israel and Iran began on 28 February, Tehran has repeatedly targeted and threatened commercial shipping, disrupting traffic through the Strait of Hormuz and driving up global prices for oil, fertiliser and other commodities.
More recently, Iran has attacked ships travelling through a US-monitored shipping corridor near Oman, outside Tehran's control, further escalating tensions. Washington has warned it could reopen the strait by force, although experts say such an operation would require a much larger military deployment.
Iran's ambassador to the United Nations, Amir Saeid Iravani, accused Washington of being the aggressor.
"The US is the aggressor, not the victim," he wrote to the UN secretary-general, according to Iran's state-run IRNA news agency.
Trump said on Tuesday that Gulf leaders had urged him to replace the proposed transit fees with increased investment in the United States.
"They said we'd love to do it a different way. We'd love to invest in the United States with billions and billions of dollars," Trump told reporters in the Oval Office.
He said he preferred that arrangement because "I don't think anybody should be able to charge a fee for the strait."
It remains unclear whether the proposed investments would be in addition to commitments announced during Trump's visit to the region last year.
The proposal to charge vessels using the strait would have marked a significant departure from longstanding US policy supporting freedom of navigation through the waterway.
In an interview with Fox News on Tuesday night, Trump warned that additional US strikes on Iran would continue over the next two days, with bridges and power plants among possible targets unless negotiations resumed.
"You better make a deal, or you're not going to have anything left," he said.
US Central Command said it carried out strikes at several locations in Iran on Tuesday. Iranian authorities acknowledged the attacks but did not provide an overall assessment of casualties or damage.
Hours after the US announced the end of its operations, Iran's Bushehr city on the Persian Gulf was hit at four locations, according to IRNA. Explosions were also reported in Ahvaz in south-western Iran and the southern port city of Bandar Abbas.
The attacks have prompted speculation that Gulf Arab states may be responding militarily to Iran without publicly acknowledging their involvement.
Kuwait separately said an Iranian strike wounded four members of its navy on Tuesday and set a building on fire.
Under the interim agreement, Iran pledged to allow free passage through the Strait of Hormuz for 60 days. However, the deal did not specify what would happen afterwards. Tehran maintains it has the right to regulate shipping through the strait and potentially impose transit fees, a position disputed by Washington.
Brent crude briefly rose above $87 a barrel on Tuesday before falling to around $78 after Trump withdrew his shipping fee proposal.
Meanwhile, regional mediators continue efforts to bring the United States and Iran back to the negotiating table.
Two regional officials, speaking on condition of anonymity because of the sensitive diplomatic efforts, said Pakistan-led mediation is working around the clock to restore the ceasefire.