Iran's chief negotiator in talks with the US said it is "not possible" for the Strait of Hormuz to be opened due to "the blatant violations of the ceasefire" by the US and Israel.

In a post on X on Wednesday, Mohammad Bagher Ghalibaf, said the "violations" include the US naval blockade of Iranian ports - which he said amounted to taking the global economy "hostage" - and "warmongering" by Israel "on all fronts".

Iran remains open to negotiations, said Iran President Masoud Pezeshkian, but he added, "breach of commitments, blockade and threats are main obstacles to genuine negotiations".

It appeared early Tuesday that the US and Iran would hold new peace talks in Pakistan this week - but they have yet to begin.

Vice-President JD Vance - due to lead the US delegation in those talks - remains in the US.

On Tuesday night, US President Donald Trump announced an extension to the US-Iran ceasefire that was due to expire on Wednesday.

White House Press Secretary Karoline Leavitt later clarified that Trump's extension is open-ended, and has no new deadline. She added that Trump is "satisfied" with the ongoing US naval blockade against Iran, and "understands Iran is in a very weak position".

"The cards are in President Trump's hands right now," she said.

Asked by reporters when the war would end, Leavitt said that it's up to Trump to decide, "and he will do so when he feels it's in the best interests of the United States and the American people".

The Iranian negotiator's latest comment comes as clashes continue in the dangerous waterway and vital global shipping route, with Iran announcing that it had "seized" two ships in the strait.

On Wednesday morning, Iran said two cargo ships were taken in the Strait of Hormuz for "inspection". The announcement follows reports of attacks on three cargo ships in the strait.

Euphoria, one of the three container ships attacked earlier in the Strait of Hormuz, appears to have dropped anchor near a port in the United Arab Emirates, according to MarineTraffic tracking data analysed by BBC Verify.

UAE-owned Euphoria was attacked eight nautical miles west of Iran, according to the maritime security firm Vanguard. No damage to the ship or injuries to crew was reported.

Iran has not commented on Euphoria, but has said it seized the other two vessels - MSC Francesca and Epaminondas - both of which reported damage resulting from the attacks.

A statement from the Iranian Revolutionary Guard Corp (IRGC) Navy said that the ships were "operating without authorisation" and committed "repeated violations", accusing them of trying to leave the Strait of Hormuz "in secret" and tampering with navigation systems.

It also warned that it is "monitoring" movements through the strait and has vowed "firm" action against the "violators".

Iranian news outlet Tasnim, which is affiliated with IRGC later posted dramatic footage of Iranian commandos raiding the two ships.

Their most recent broadcast positions indicates neither has moved far since the attacks occurred.

However, MarineTraffic data indicates Euphoria returned to sailing southwards after the reported time it was attacked, ending up about 13 nautical miles from the port of Khor Fakkan at around 14:00 BST.

Greek Foreign Minister Giorgos Gerapetritis later confirmed that the Epaminondas, a Greek-owned ship, had been attacked.

"I can confirm that there was an attack against the Greek cargo ship, but I cannot confirm that this has been seized by the Iranians," Gerapetritis told CNN.

Also on Wednesday, the US Defense Department announced that the US Secretary of the Navy would depart his post "effective immediately".

No reason was given for John Phelan's ouster. It comes just weeks after US Defense Secretary Pete Hegseth asked Army Chief of Staff Randy George to step down from his post. Navy Undersecretary Hung Cao will serve as acting secretary.

The White House lack of a timeline - either for a return to negotiations in Pakistan or to kinetic strikes against Iran - is likely strategic. It gives the Trump administration significant flexibility to let the blockade and the economic stranglehold on Iran bite.

Leavitt said this will allow "pragmatists" in Iran to come up with a peace proposal without pushback from hardliners.

At the same time, it allows Trump to avoid a return to full-scale military action that many Americans are weary of, and that could upset already nervous global markets.

In her remarks to reporters at the White House, Leavitt also said that the US does not consider Iran's seizure of two ships in the Strait of Hormuz to be a violation of the ceasefire.

"These were not US ships, these were not Israeli ships," she said.