Divisions over responsibility for last week’s attack on two oil tankers in the Gulf of Oman deepened this weekend amid warnings over the danger of a major confrontation in the region, despite hints by Donald Trump about possible negotiations with Iran.

Politicians in Britain traded angry blows over the incident, after the Labour leader, Jeremy Corbyn, questioned whether there was “credible evidence” that Iran had attacked the two ships as they passed by its coast on Thursday, rebuffing a Foreign Office assessment that it was “almost certain” that a “branch of the Iranian military” had carried out the strikes.

“Britain should act to ease tensions in the Gulf, not fuel a military escalation that began with US withdrawal from the Iran nuclear agreement,” Corbyn tweeted. “Without credible evidence about the tanker attacks, the government’s rhetoric will only increase the threat of war.”

The comments drew an immediate rebuke from the foreign secretary, Jeremy Hunt, who described them as “pathetic and predictable”. Earlier the FCO had said: “No other state or non-state actor could plausibly have been responsible,” and pointed to a “recent precedent for attacks by Iran against oil tankers”.

The row came as tensions between the regional heavyweight and Washington remained high, three days after an attack that sent tremors through oil markets and sparked fears of widespread disruption to the global oil trade, much of which passes through Gulf waters.

Iran has denied carrying out the attacks – the second strikes in a month on Gulf shipping – disputing footage released by the US military that purports to show Iranian naval commandos removing an unexploded mine from the hull of one of the crippled tankers.

US defence officials said on Friday that prior to the attack, Iranian forces had fired an anti-aircraft missile at a US drone that had been monitoring their activity close to the tankers in the Gulf of Oman.

Officials said the Reaper drone took images of Iranian vessels closing in on the two tankers that were attacked but did not say whether there was any visual evidence of the attack itself.

President Trump has sent mixed signals over how he wants to address the crisis, which erupted as the Japanese prime minister, Shinzo Abe, was in Tehran, carrying an offer of talks from the White House.

After Iran’s supreme leader, Ali Khamenei, rejected the offer, Trump disowned Abe’s mission and tweeted that it was “too soon to even think about making a deal” with Iran’s leaders. “They are not ready, and neither are we!”

Facebook Twitter Pinterest Videograb released by US Central Command purports to show an Iranian navy patrol boat in the Gulf of Oman approaching a Japanese tanker and removing an unexploded mine. Photograph: AFP/Getty Images

However, in the same interview on his favourite television talk show, Fox & Friends, on Friday morning, in which he said “Iran did it”, the US president also said: “They’ve been told in very strong terms we want to get them back to the table.”

Hunt was among several candidates for the Tory leadership to attack Corbyn for his remarks. Michael Gove accused the Labour leader of “failing to stand up for our values of freedom and democracy”. Dominic Raab accused him of “anti-American prejudice”. Labour MP John Mann, a leading party critic, also denounced his leader’s comments.

Emily Thornberry, the shadow foreign secretary, appeared to soften Labour’s stance on the issue, saying that there needed to be further “processes” to establish whether Iran was behind the attack. She suggested that Iran could have carried out the tanker attack after taking the “bait” of western sanctions.

“These are extremely dangerous developments and we really have to pause and think about where we are going next,” she told BBC Radio 4’s Today programme. Thornberry insisted that the main issue was avoiding “British forces being drawn into a conflict of that size”.

“We’ve got to give up on this idea that if the United States go into war, especially one engineered by the likes of John Bolton and the neocons, we have to stop and say there are times when we don’t just follow,” Thornberry said.

“We made a dreadful mistake when it came to Iraq and we must not make the same mistake again.”

Saudi Arabia’s crown prince blamed Iran for attacks, according to an interview with the Saudi-owned Asharq al-Awsat newspaper.

“The Iranian regime did not respect the Japanese prime minister’s visit to Tehran and while he was there replied to his efforts by attacking two tankers, one of which was Japanese,” the newspaper quoted Crown Prince Mohammed bin Salman as saying on its Twitter account.

The head of the Arab League has called on the Iranians to “be careful and reverse course”. In New York, the league’s secretary general Ahmed Aboul Gheit said: “We believe that responsibilities need to be clearly defined. The facts will be revealed, I am sure, it’s only a matter of time.

“My call to my Iranian – and I call them Iranian – brothers: Be careful and reverse course because you’re pushing everybody towards a confrontation that no one would be safe if it happens.”

And the United Arab Emirates’ top diplomat said evidence indicates that recent attacks against oil tankers inside UAE waters were “state-sponsored”. But Russia has warned against rushing to assign blame for the attacks and accused the US of using its accusations against Iran to stoke tensions in the region.