JD Vance has warned Iran not to “try and play” the US at talks planned for Saturday in Islamabad, while Tehran said it would not take part until Israel stopped bombing of Lebanon.

The US vice-president made the comments as he boarded a plane to Pakistan for negotiations that could determine whether a ceasefire holds or the war on Iran resumes with grave implications for the global economy.

With hours to go before the talks were scheduled to start, doubts remained as to whether they actually would.

Mohammad Baqer Qalibaf, Iran’s parliamentary speaker and the co-leader of the country’s delegation, said on X on Friday: “Two of the measures mutually agreed upon between the parties have yet to be implemented: a ceasefire in Lebanon and the release of Iran’s blocked assets prior to the commencement of negotiations. These two matters must be fulfilled before negotiations begin.”

It was unclear on Friday evening whether Qalibaf and Abbas Araghchi, Iran’s foreign minister, were still planning to fly to Islamabad to lead their delegation. It was reported last month that Israel had taken Qalibaf and Araghchi off the target list of its bombing campaign at Washington’s request.

Donald Trump fuelled the uncertainty by saying US forces were rearming and ready to return to the attack if the negotiations failed.

“We have a reset going. We’re loading up the ships with the best ammunition, the best weapons ever made – even better than what we did previously and we blew them apart,” the US president told the New York Post. “And if we don’t have a deal, we will be using them, and we will be using them very effectively.”

Later on Friday, Trump followed up his threats with a post on his own social media site declaring: “The Iranians don’t seem to realize they have no cards, other than a short term extortion of the World by using International Waterways. The only reason they are alive today is to negotiate!”

The Iranians and the Pakistani mediators say the two-week ceasefire agreement struck by the US and Iran on Tuesday night included Lebanon. Trump and Israel’s prime minister, Benjamin Netanyahu, say this is not the case, and Israel has continued to bomb Lebanon in its offensive against Hezbollah, Iran’s closest ally in the region, even after Netanyahu said he was ready to start peace talks with the Lebanese government.

More than 300 Lebanese citizens have been killed by Israeli bombing since the ceasefire started. The country’s president, Joseph Aoun, said on Friday that 13 state security personnel had been killed in an Israeli strike on a government building in the southern city of Nabatieh.