"Since Sunday, when the Iranian delegation returned to Tehran, several messages have been exchanged through Pakistan," said foreign ministry spokesman Esmaeil Baqaei in a weekly press briefing.

"Today, we are very likely to receive a Pakistani delegation as a continuation of the discussions in Islamabad," he added.

The US-Iran negotiations at the weekend in Pakistan took place against the backdrop of a fragile two-week ceasefire announced days earlier, but they failed to produce a deal to end the war.

The talks, which lasted around 21 hours, saw the US delegation led by Vice President JD Vance and the Iranian side headed by parliament speaker Mohammad Bagher Ghalibaf.

The main sticking points were not officially disclosed at the time, but US President Donald Trump later castigated Iran for not opening the Strait of Hormuz, which has been all but closed since the outbreak of war on February 28.

Trump also said Iran had refused to concede on the issue of its nuclear programme.

News reports have since said Washington sought a 20-year suspension of Iran's uranium enrichment and that Iran, in turn, proposed suspending its nuclear activity for five years -- an offer US officials rejected.

On Wednesday, Baqaei said some of the US demands during the talks were "unreasonable and unrealistic", without elaborating.

He insisted on Iran's right to peaceful use of nuclear energy, saying it could not be "taken away under pressure or through war".

The level of enrichment, he said, remains "negotiable" and "Iran should be able to continue enrichment in accordance with its needs".

Baqaei criticised a US naval blockade on Iranian ports in place since Monday, saying it "will not succeed".

He said Iran "will not enter into any negotiations just to accept the American conditions".