Iran’s Revolutionary Guards have threatened to target US sites in the Middle East if its tankers come under fire, Iranian media reported on Saturday, as Washington was left waiting for Tehran’s response to its latest negotiating position.

“Any attack on Iranian tankers and commercial vessels will result in a heavy attack on one of the American centres in the region and enemy ships,” the force said, a day after US strikes on two Iranian tankers in the Gulf of Oman.

On Sunday morning the UK Maritime Trade Operations centre said a ship caught fire after being hit by an unknown projectile off the coast of Qatar.

The attack caused a small fire on the bulk carrier, which was extinguished. It happened 23 nautical miles (43km) north-east of Qatar’s capital, Doha, UKMTO said.

Donald Trump had said on Friday that he was expecting Iran’s answer to Washington’s latest proposal for a peace deal “supposedly tonight”.

But if Tehran sent Pakistani mediators a response, there was no public sign of it, and Iran’s foreign minister Abbas Araghchi reportedly questioned the reliability of US leadership.

“The recent escalation of tensions by American forces in the Persian Gulf and their numerous actions in violating the ceasefire have added to suspicions about the motivation and seriousness of the American side in the path of diplomacy,” he said in a call with his Turkish counterpart, according to Iran’s ISNA news agency.

On Friday, a US fighter jet fired on and disabled two Iranian-flagged tankers that Washington accused of challenging its blockade of Iran’s ports. An Iranian military official told local media the navy had responded with strikes.

That followed a flare-up the night before in the strait of Hormuz, the vital international sea lane that Iran is seeking to control in order to extract tolls and wield economic leverage over the US and its allies.

The US says it is unacceptable for Tehran to control the key oil route.

Washington has sent Iran, via Pakistani mediators, a proposal to extend the truce in the Gulf to allow for talks on a final settlement of the conflict launched 10 weeks ago with US-Israeli strikes on Iran.

A reporter for French broadcaster LCI, Margot Haddad, said on Saturday that Trump had told her in a brief interview he still expected to find out Iran’s answer “very soon”.

Iran’s foreign ministry spokesperson on Friday said the proposal was still “under review”.

The US secretary of state, Marco Rubio, on Saturday met with the leader of Qatar, a key intermediary for Washington in dialogue with Iran, discussing “continued close coordination to deter threats and promote stability and security across the Middle East”, the state department said.

Qatar’s Sheikh Mohammed bin Abdulrahman Al Thani met the previous day with the US vice-president, JD Vance, to discuss the Pakistani-led efforts to broker a permanent peace.

Iran has attacked sites in Qatar during the war, pointing to the wealthy emirate’s role as host of a major US airbase.

Oil slick appears off Kharg Island

Meanwhile, satellite images have shown an apparent oil slick spreading off the coast of Iran’s Kharg Island, a key oil export terminal for Iran.

It was not immediately clear what caused the apparent spill, which was off the island’s west coast and appeared to cover more than 20 square miles (52 square kilometres), according to global monitor Orbital EOS.

A UK-based non-governmental organisation, the Conflict and Environment Observatory, told AFP that by Saturday the slick was “much reduced”, and may have been caused by leaking oil infrastructure.

Kharg Island is at the heart of Iran’s oil export industry, a linchpin of its battered economy, and lies in the Gulf far north of the narrow strait of Hormuz.

After the start of the war on 28 February, Iran largely closed the strait, throwing global markets into turmoil and driving up oil prices.

The US later imposed its own blockade of Iranian ports in response, and Trump this week abandoned a short-lived US naval operation to reopen the strait to commercial shipping.

Fighting on Lebanon front

A parallel ceasefire on the war’s Lebanon front is also under strain amid daily exchanges of fire between Israel and the Iran-backed Hezbollah.

Authorities said at least nine people were killed in Israeli strikes in southern Lebanon on Saturday, while state media reported air raids targeting a highway south of Beirut, outside the militant group’s traditional strongholds.

The fresh attacks were some of the most intense since the start of a three-week-old ceasefire between Israel and Hezbollah.

Hezbollah said it targeted troops in northern Israel with drones on at least two occasions in response to the continued strikes.

Israel’s military said several explosive drones were launched into Israeli territory, with one army reservist severely wounded and two others moderately injured.

The fresh strikes come as Lebanon and Israel, officially at war since 1948, are to hold direct negotiations in Washington next week, which Hezbollah vehemently opposes.