President Donald Trump on Sunday accused Iran of a “total violation” of a cease-fire after Iranian forces fired on ships near the Strait of Hormuz, and renewed a threat to strike the country’s infrastructure if it did not accept U.S. terms.

“Iran decided to fire bullets yesterday in the Strait of Hormuz — A Total Violation of our Ceasefire Agreement!” Trump wrote on Truth Social. He warned that unless Iran agreed to a deal, the United States would “knock out every single Power Plant, and every single Bridge, in Iran.”

Trump said U.S. envoys would arrive in Pakistan on Monday evening for a new round of talks, the first official confirmation that negotiations would resume after an earlier round ended without a breakthrough.

But Iran rejected the prospect of new negotiations, according to its state news agency IRNA, which said the decision stemmed from what it described as Washington’s “excessive demands,” “unrealistic expectations,” and the ongoing naval blockade. IRNA did not cite a specific official in its report.

Earlier on Sunday, a White House official told TIME that Vice President JD Vance, who led the previous round of talks with Iran, was planning to once again lead the U.S. delegation in Islamabad. The plan marked a shift after Trump told a reporter that Vance would not make the trip.

Special Envoy Steve Witkoff and Jared Kushner, the president’s son-in-law and a former adviser on Middle East negotiations, would also attend, the official said.

The renewed push comes amid concerns raised by former diplomats in recent reporting by TIME, who questioned whether Witkoff and Kushner have the experience needed to secure a deal and warned that missteps could prolong the conflict.

The Strait of Hormuz, a flashpoint in the talks, remained effectively closed. Tracking data showed almost no vessel movement through the strait after Saturday’s attacks, when at least two ships reported being fired upon by gunboats linked to Iran's Islamic Revolutionary Guard Corps (IRGC).

Iranian officials said they would not allow ships to pass while the U.S. blockade remained in place. “It is impossible for others to pass through the Strait of Hormuz while we cannot,” Iran’s parliamentary speaker, Mohammad Baqer Qalibaf, said in remarks broadcast on state television, according to the Associated Press.

The confrontation has raised fears of further escalation in a waterway that normally carries roughly one-fifth of the world’s oil supply. Iran’s closure of the strait has stranded hundreds of vessels in the Gulf and driven up shipping costs, with crews avoiding the area amid fears of attacks.

In a sign of limited exceptions to the shutdown, the cruise operator Tui said on Sunday that two of its ships, Mein Schiff 4 and Mein Schiff 5, had passed through the strait after receiving approval from relevant authorities and would proceed to the Mediterranean.

Iranian officials confirmed that new U.S. proposals had been delivered through Pakistani mediation and were under review. Iran’s Supreme National Security Council said the country had not yet responded.

Citing an unnamed official involved in the mediation efforts, the Associated Press reported that mediators were “finalising the preparations” and that US security teams were “already on the ground.”

The main sticking points remain Iran’s nuclear program, particularly its stockpile of enriched uranium, and control over the Strait of Hormuz.

“There is still a big distance between us,” said Qalibaf, Iran’s chief negotiator, while insisting that Iran remained committed to diplomacy.

Security measures were tightened in Islamabad ahead of the expected talks, with Pakistani authorities restricting movement near the site of last week’s discussions. 

U.S. Central Command (CENTCOM) said on Saturday that American forces were continuing to enforce the naval blockade, with 23 ships complying with orders to turn around since it began. The U.S. military is now preparing to board Iran-linked oil tankers and seize commercial vessels in international waters in the coming days, The Wall Street Journal reported, citing U.S. officials.

The standoff has intensified pressure on negotiations aimed at ending a conflict that began on Feb. 28, when the United States and Israel launched strikes on Iran over its nuclear and missile programs. The war has since killed several thousand people across Iran, Lebanon and other parts of the region and displaced millions.

Now in its eighth week, the conflict has severely disrupted global energy markets. Prices tumbled when the strait briefly reopened on Friday, but the latest closure is likely to renew volatility as markets reopen. 

— Rebecca Schneid contributed to this report