Jeremy Corbyn has questioned whether the government has “credible evidence” to show Iran is behind the attacks on two oil tankers in the Gulf of Oman.
Foreign Secretary Jeremy Hunt said responsibility for Thursday’s attacks “almost certainly” lies with the Iranian regime.
But the Labour leader tweeted that there was no evidence for this.
Mr Hunt responded that Mr Corbyn’s comments were “pathetic” and said he should back British intelligence.
It is the second time in the past few weeks that tankers appear to have been attacked in the region and comes amid escalating tension between Iran and the United States.
The US military released video footage which it said proved Iran was behind Thursday’s attacks on the Norwegian and Japanese tankers – something Iran has categorically denied.
Although Iran has denied being behind the explosions, experts believe it could be a response to US sanctions intended to stop other nations from purchasing Iranian oil.
After the sanctions were tightened last month, Iran announced that “if it could not export its oil, no other country would be allowed to export theirs”, Dr Aniseh Bassiri Tabrizi, from the Royal United Services Institute, said.
The UK Foreign Office said it was “almost certain” that a branch of the Iranian military – the Islamic Revolutionary Guard Corps – attacked the two tankers on 13 June, adding that “no other state or non-state actor could plausibly have been responsible”.
“These latest attacks build on a pattern of destabilising Iranian behaviour and pose a serious danger to the region,” Mr Hunt said.
However, in a tweet, Mr Corbyn questioned that assessment and said the UK should ease tensions in the region, not fuel a military escalation.