Iran has protested to the UK’s ambassador in Tehran after being accused of involvement in attacks on two oil tankers in the Gulf of Oman.
Iran has denied being behind Thursday’s explosions in the key shipping route.
But UK Foreign Secretary Jeremy Hunt has backed the US assessment, saying Iran is “almost certainly” responsible.
Amid growing tensions in the region, a British-Iranian woman jailed in Tehran has begun a new hunger strike, demanding her unconditional release.
Mother-of-one Nazanin Zaghari-Ratcliffe was jailed for five years in 2016 after being convicted of spying – which she denies.
Her husband, Richard Ratcliffe, is joining her in refusing food and has set up a tent outside the Iranian embassy, where he plans to stay while his wife is on hunger strike, to protest against her “unfair imprisonment”.
A UK Foreign Office official said the meeting with Britain’s ambassador, Rob Macaire, was not a formal diplomatic summons.
But BBC diplomatic correspondent Caroline Hawley said Iran is “clearly angry” at the British accusations and “made its displeasure known” through the meeting with a senior foreign ministry official.
Thursday’s attacks on Norwegian and Japanese vessels was the second time in the past few weeks that tankers appear to have been targeted 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 the incident. US President Donald Trump cited it, saying it shows Iranian forces removing an unexploded mine off the hull of one of the ships – hours after the initial detonations.
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”.
However, Labour leader Jeremy Corbyn has questioned whether the UK has “credible evidence” for this assessment.
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.
Saudi Arabia has also blamed its rival Iran for the attacks, along with the US.
UN Secretary General Antonio Guterres said the truth needed to be “clearly established”, while Russia has warned against drawing “hasty conclusions”.
The blasts came a month after four oil tankers were damaged in an attack off the coast of the United Arab Emirates. The US blamed Iran for that attack, but did not produce evidence. Iran also denied those accusations.
Tensions between the US and Iran have escalated significantly since President Trump took office in 2017.
He abandoned a nuclear deal that was brokered by Barack Obama’s administration and significantly tightened sanctions on Iran.
Meanwhile Mr Hunt has urged Iran to release jailed British-Iranian Mrs Zaghari-Ratcliffe, saying “whatever the disagreements you may have with the United Kingdom, there is an innocent woman at the heart of this”.