The US will not lift its blockade on Iranian ports until a deal has been reached with Tehran, US President Donald Trump has said, amid continuing uncertainty over whether fresh talks to end the war will take place.

The blockade, which began a week ago, is "absolutely destroying Iran", Trump wrote on his social media platform Truth Social, adding his country was winning the conflict "by a lot".

His comments come with the temporary US-Iran ceasefire set to end on Wednesday, but with no certainty over whether a second round of peace talks will go ahead in Pakistan.

There is tightened security in Pakistan's capital in anticipation of a meeting. But US Vice President JD Vance, set to lead the US delegation, has not yet left Washington, while Iran says it has not yet decided whether to attend.

Since the blockade began, US forces have directed 27 vessels to turn around or return to an Iranian port, according to US Central Command (Centcom).

The US also intercepted and seized an Iranian-flagged cargo ship for the first time in the conflict, after it tried to get through the blockade on Sunday.

Videos shared by Centcom were said to show the ship being warned before troops repelled onto the vessel.

Tehran deemed it an "act of piracy" and a violation of the fragile ceasefire between the two countries.

Iran has maintained its own blockade on the Strait of Hormuz, a key shipping route, for nearly two months, causing global energy prices to soar.

It was briefly reopened on Saturday but quickly closed again, following reports of vessels in or near the strait, including a tanker, being targeted by Tehran.

Trump said Iran had "decided to fire bullets" and called it a "total violation" to the ceasefire agreement.

Iran said it would keep the route shut until the US stopped the blockade of its ports.

There are indications a second round of peace talks between the US and Iran will go ahead, despite Tehran refusing to confirm whether it will send a delegation.

Following the first round of talks earlier this month US Vice-President J D Vance said the US "could not get to a situation where the Iranians were willing to accept our terms", and Iran's foreign ministry urged Washington to refrain from "excessive demands and unlawful requests".

The potential second round comes at a crucial moment. Sources told the BBC on Monday afternoon that the US delegation would be leaving "soon" but did not specify a time, while officials told the New York Times that they would depart on Tuesday.

Later on Monday, an Iranian foreign ministry spokesperson said that, "so far", Tehran had "no plans" to attend.

Vance is expected to be joined by special envoy Steve Witkoff and Trump's son-in-law and adviser, Jared Kushner, as in the previous round of talks.

It is not clear who - if anyone - from Iran's side will be showing up.

However, in Islamabad, there are signs of preparation for the talks.

Guests at the city's Serena Hotel, where the previous round was held, have been told to leave in preparation for meetings, while police announced the closure of key roads due to the arrival of foreign delegations.

A senior government official told Reuters news agency that Pakistan was confident it could get Iran to attend the talks.

Speaking to Radio 4's PM programme, the BBC's Chief International Correspondent Lyse Doucet, who is in Tehran, said that although the situation was unpredictable, there was a better chance the talks would happen.

"There is one rule in diplomacy, which is, you don't want to be the one blamed for something breaking down.

"If JD Vance is going to be in Islamabad, it will be really hard for the Iranians to not show up.

"And I think the telephone lines are burning with the Pakistanis trying to ensure that both sides get there, because the venue is ready, the security is in place, they are just waiting for teams to arrive."