US Vice President JD Vance is expected to arrive in Islamabad on Wednesday to lead the second round of indirect talks involving Iran, according to sources close to the mediation process cited by Al Jazeera, amid growing uncertainty over whether the Iranian side will participate.

Sources said Vance will depart Washington on Tuesday evening and is expected to land in the Pakistani capital around midday on Wednesday, with the discussions reportedly scheduled to take place the same day.

Preparations for the meeting are said to be underway, with reports indicating that several US military aircraft have already arrived in Pakistan in connection with the arrangements for the delegation.

However, Iran’s participation remains unclear. Iranian state media has already denied reports that any delegation has travelled to Islamabad for talks, dismissing earlier speculation as “unfounded” and insisting that no representatives—senior or otherwise—are currently engaged in such negotiations.

Adding to the uncertainty, Iranian Parliament Speaker Mohammad Bagher Ghalibaf reiterated that Tehran does not accept negotiations conducted under threat or pressure, reinforcing long-standing Iranian conditions for any diplomatic engagement with Washington.

The apparent contradiction between US planning and Iranian public positions has raised doubts over whether the scheduled meeting will proceed as planned.

Pakistan, which has played a mediating role in facilitating earlier contacts between the two sides, is continuing efforts to keep the diplomatic channel open. However, observers note that the talks remain fragile, with both timing and participation still in question.

The situation comes at a sensitive moment, as broader regional tensions and ceasefire arrangements linked to earlier rounds of dialogue face increasing uncertainty.

Concerns are mounting over the durability of the ceasefire between the United States and Iran after Washington said it had seized an Iranian cargo vessel accused of breaching its maritime blockade, prompting a warning of retaliation from Tehran.

According to the U.S. military, forces opened fire on an Iranian-flagged ship following a prolonged standoff in waters near the Strait of Hormuz, disabling its engines before troops boarded the vessel. U.S. Central Command said marines descended from helicopters and took control of the ship.

U.S. President Donald Trump confirmed the operation in a social media post, saying American forces had “full custody” of the vessel and were inspecting its cargo.

Iranian authorities condemned the seizure, describing it as “armed piracy.” A military spokesperson, quoted by state media, warned that Iran’s armed forces would respond. Officials said the ship had been en route from China to the Iranian port of Bandar Abbas.

Ceasefire and talks in doubt

The incident has cast doubt on efforts to sustain a fragile ceasefire set to expire on Tuesday. Hopes for a broader agreement also appeared uncertain after Iranian state media reported that Tehran would not take part in a planned second round of negotiations.

Iranian officials cited ongoing U.S. blockade measures, escalating rhetoric, and what they described as shifting demands from Washington. First Vice President Mohammadreza Aref said Iran would not accept restrictions on its oil exports while others benefited from open energy markets.

“If Iran’s oil is restricted, others should not expect full security,” he said in remarks carried by state media.

Preparations for uncertain negotiations

Despite the tensions, diplomatic activity is continuing. U.S. envoys are expected to travel to Islamabad, which has been acting as a key mediator. However, uncertainty remains over the composition of the U.S. delegation and whether talks will proceed as planned.

Security measures in Islamabad have been stepped up ahead of the anticipated visit, with restrictions imposed on transport and heightened protection around key venues.

Iran’s parliament speaker Mohammad Baqer Qalibaf had earlier indicated that while some progress had been made in initial discussions, significant gaps remain, particularly over nuclear issues and maritime security.

Global market impact

The developments have unsettled global markets. Oil prices rose sharply amid fears that the ceasefire could collapse, further disrupting flows through the Strait of Hormuz — a critical route for roughly one-fifth of the world’s oil supply.

The conflict, now in its eighth week, has already caused major disruptions to regional energy production. Countries including Saudi Arabia, Iraq, Kuwait and the United Arab Emirates have seen significant declines in output.

Escalating rhetoric

Tensions have been further heightened by increasingly sharp rhetoric. President Trump has warned that the United States could target key Iranian infrastructure if negotiations fail, while Iranian officials have threatened retaliatory strikes against regional energy and utility facilities if attacked.

The war, which began in late February, has triggered one of the most severe shocks to global energy markets in recent history and raised fears of broader regional escalation.

U.S. President Donald Trump has accused Iran of violating a ceasefire agreement in the Strait of Hormuz and warned of sweeping military consequences if tensions escalate further.

In a message posted on Truth Social, Trump claimed that Iranian forces “fired bullets” in the vital shipping corridor, describing the incident as a “total violation” of the ceasefire. He alleged that the gunfire was directed at a French vessel and a United Kingdom-flagged freighter, though the claims have not been independently verified.

Trump said U.S. representatives would travel to Islamabad for negotiations, indicating that diplomatic efforts are continuing despite rising tensions.

The comments come amid heightened friction between Washington and Tehran over maritime security. The Strait of Hormuz, a critical chokepoint for global oil shipments, has long been a focal point of confrontation between Iran and Western powers.

In his post, Trump also claimed Iran had moved to close the waterway, while asserting that a U.S. “blockade” had already effectively halted traffic. He argued that such a closure would primarily harm Iran, estimating losses of up to $500 million per day.

He added: “In fact, many Ships are headed, right now, to the U.S., Texas, Louisiana, and Alaska, to load up, compliments of the IRGC, always wanting to be ‘the tough guy!’.”

In his sharply worded warning, Trump said that if Iran does not accept what he described as a “fair and reasonable deal,” the United States could target key infrastructure, including power plants and bridges.

“We’re offering a very fair and reasonable DEAL, and I hope they take it because, if they don’t, the United States is going to knock out every single Power Plant, and every single Bridge, in Iran.

“NO MORE MR. NICE GUY! They’ll come down fast, they’ll come down easy and, if they don’t take the DEAL, it will be my Honor to do what has to be done, which should have been done to Iran, by other Presidents, for the last 47 years. IT’S TIME FOR THE IRAN KILLING MACHINE TO END!” he wrote.

Iran has not yet publicly responded to the remarks.

Analysts note that any escalation around the Strait of Hormuz carries significant global risks, given the route’s central role in international energy supplies.