Iranian officials say they have reversed the reopening of the strait of Hormuz and reimposed restrictions on the vital shipping lane after the US said it would not end its blockade of Iranian ports.

A UK maritime agency reported that Islamic Revolutionary Guard Corps (IRGC) ships had fired at a tanker as it attempted to pass through the strait on Saturday. Reuters reported an Indian-flagged vessel carrying crude oil had also been attacked while in the waterway.

Iran’s Khatam al-Anbiya joint military command said on Saturday that Tehran had restored the strait to its “previous status” and was now “under strict management and control by the armed forces”.

Iran said the restrictions would remain if Washington did not “ensure full freedom of navigation for vessels travelling from Iran to destinations and from destinations to Iran”. This was reiterated by the country’s deputy foreign minister, Saeed Khatibzadeh, and the IRGC’s navy command.

Iran’s top negotiator, Mohammad Bagher Ghalibaf, said on Saturday that the recent talks with the US had made progress but gaps remained over nuclear issues and the strait of Hormuz. “We have had progress but there is still a big distance between us,” he told state media, referring to talks last weekend. “There are some issues on which we insist … They also have red lines. But these issues could be just one or two.”

President Donald Trump said the US was having “very good conversations” with Tehran but warned against “blackmail” over the key shipping channel. He later praised war ally Israel in a social media post, adding that other allies had “shown their true colours in a moment of conflict and stress”.

Neither side offered any specifics about the state of negotiations on Saturday, days before a fragile ceasefire in the US-Israeli war against Iran is set to expire.

The war, now in its eighth week, has killed thousands, spread to Israeli attacks in Lebanon and sent oil prices surging because of the closure of the strait, which usually carries a fifth of the world’s oil shipments.

Speaking to journalists on the sidelines of a Turkish diplomatic forum in Antalya, Iranian deputy foreign minister Khatibzadeh said the US “cannot impose their will to do a siege over Iran, while Iran, with good intention, is trying to facilitate safe passage through the strait of Hormuz”.

In a post on X, the IRGC’s navy command wrote: “As long as the movement of vessels from Iran and to Iran is under threat, the status of the strait of Hormuz will remain as it was previously. Any breach of commitments by the United States will receive an appropriate response.”

Iran officially closed the strait on 4 March in response to US-Israeli airstrikes on the country, and declared it back open on Friday after a 10-day ceasefire deal was agreed between Israel and Lebanon, as part of wider negotiations to achieve peace in the region.

The UK’s Maritime Trade Operations Centre said it had received a report from a tanker that had been approached and then fired on by “two IRGC gunboats” 20 nautical miles north-east of Oman. The captain said there had been no radio warning beforehand. The agency added that the tanker and crew were reported safe, and authorities were investigating the incident.

The announcement of Iran’s U-turn came the day after Donald Trump said the US blockade would “remain in full force” until a permanent peace deal with Tehran was reached. The US president also said that the temporary ceasefire with Iran, brokered by Pakistan and due to expire on Wednesday, may not be extended.

US and Iranian delegations are expected to hold a second round of peace talks, although the timing is yet to be confirmed. Agence France-Presse reported that the Egyptian foreign minister said on Saturday there were hopes for a deal “in the coming days”.

“We hope to do so [reach an agreement] in the coming days,” Badr Abdelatty said, adding: “Not only us in the region, but the whole world is suffering from the continuation of this war”.

Before Iran’s reversal, at least eight oil and gas tankers had passed through the strait in the brief window when it was open early on Saturday, according to maritime tracking data.

About 20% of the world’s oil and liquefied natural gas passes through the narrow strait, which has become a focal point of the US-Israeli war on Iran. Its closure has driven up energy prices around the world.

In Lebanon, the Israeli military said on Sunday that one soldier was killed during combat in the south, adding that nine soldiers were wounded, including one who was severely injured.