"The reason for the recent strikes over the course of the last several days is because Iran violated the Memorandum of Understanding that we struck with them," White House spokeswoman Karoline Leavitt said on Thursday.
"Specifically, in the memorandum of understanding that they signed, they were not to fire on commercial vessels moving through the Strait of Hormuz, and unfortunately they have made the tragic decision for them to do that.
Leavitt said that the Strait of Hormuz is open for ships that are not travelling to or from Iranian ports and that the US navy remains there "to ensure that can take place".
Iran and the US exchanged intensified fire on Thursday in a week-long escalation that has all but torn up last month's truce although Iran's release of a US citizen pointed towards a path to avert the resumption of all-out war.
For the first time since an MoU paused fighting, the US launched two big waves of air strikes in a single day on Wednesday, mostly on targets near Iran's southern coast, and kept firing on Thursday.
Iran responded with missiles and drones targeted at US military bases in neighbouring countries, including a barrage at a recently expanded air base in Jordan.
After Iran resumed its blockade of the Gulf through the Strait of Hormuz, the US again blockaded Iranian ports from Wednesday.
The US military said it fired on a tanker near Iran's Kharg Island, with Hellfire missiles hitting its smokestack.
On Thursday evening, US projectiles struck Qeshm Island and near Bandar Abbas - home to Iran's largest port and key navy and Revolutionary Guards facilities - both on the Strait of Hormuz, Iranian state media said.
For one of its next moves, Iran has signalled it could prod its Houthi allies in Yemen to close another key strait: the Bab al-Mandeb at the mouth of the Red Sea.
Sources told Reuters Iran had already told the Houthis to shut it if the US carries out threats to attack Iran's infrastructure.
The week of increasingly intense fire has tested the limits of escalation that both sides set during four months of fighting before last month's truce.
But as the attacks unfurled, US President Donald Trump hailed the release of a US citizen in Iran as a "gesture of goodwill".
Human rights lawyer Jared Genser identified her as Dena Karari, who he said had been "trapped in Iran since December 2024 on bogus charges" and was "now safe and travelling back to the United States".
There was no comment from Iran on the case.
5°C