Pakistan confirmed the arrival of a delegation of Iranian negotiators ahead of talks on Saturday with the U.S. to end the six-week-old war Washington and Tel Aviv have led against Tehran.

The negotiations will seek to cement a two-week ceasefire that began Tuesday but which has come under strain as Iran continues to block most shipping traffic through the Strait of Hormuz, the world’s most critical chokepoint for oil and gas supplies.

Pakistan’s foreign ministry said the Iranian delegation led by parliamentary speaker Mohammad Bagher Ghalibaf and Foreign Minister Abbas Araghchi arrived in the capital Islamabad late Friday.

Pakistan’s Deputy Prime Minister and Foreign Minister Mohammad Ishaq Dar “expressed the hope that parties would engage constructively, and reiterated Pakistan’s desire to continue facilitating the parties towards reaching [a] lasting and durable solution to the conflict,” Pakistan’s foreign ministry said in a post on X.

But question marks hang over the ceasefire and the outcome of the talks. Ghalibaf warned Friday that scheduled negotiations to end the war with the United States cannot begin unless Israel halts attacks on Lebanon and unless the U.S. releases Tehran’s frozen assets.

Ghalibaf issued that ultimatum after an American delegation led by Vice President JD Vance left for Islamabad for the talks.

“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,” Ghalibaf said in an X post.

“These two matters must be fulfilled before negotiations begin,” he wrote.

Earlier Friday, Vance told reporters he thinks the negotiations will be “positive,” while warning Iran not to “play us.”

Vance’s team landed in Islamabad early Saturday and was met by U.S. Special Envoy Steve Witkoff and President Donald Trump‘s son-in-law, Jared Kushner.

Meanwhile, Trump has expressed frustration with Iran continuing to block most shipping traffic through the Strait of Hormuz.

The strait is the world’s most vital shipping route for oil. Before the war, 20% of the world’s crude was transported through that passage.

In an announcement Tuesday evening, Trump said that the U.S. would agree to a two-week suspension of hostilities subject to Iran agreeing to a complete and immediate reopening of the Strait of Hormuz.

But since then, vessel traffic through the strait remains nearly as tightly throttled as it has been since the war began on Feb. 28.

In a Truth Social post on Thursday evening, Trump fumed, “There are reports that Iran is charging fees to tankers going through the Hormuz Strait — They better not be and, if they are, they better stop now!”

Iran “is doing a very poor job, dishonorable some would say, of allowing Oil to go through the Strait of Hormuz,” the president wrote in a follow-up post. “That is not the agreement we have!”