This Iranian tanker was seized last week by British forces.
The Grace 1 was suspected of breaking sanctions by taking oil to Syria.
Iran threatened retaliation.
Now this: U.S. officials say that on Wednesday (July 11) a UK oil tanker, the British Heritage, was approached in the Gulf by five boats beleived to be from Iran's Revolutionary Guards and asked it to stop in Iranian waters.
But, the officials say the HMS Montrose, a British warship "pointed its guns at the boats and warned them" and so they then backed off.
The U.S. claim has been backed up by the British government but rejected by the Revolutionary Guards,and Iran's foreign minister who says the claim is worthless.
Since Washington ratcheted up sanctions against Iran tensions have spiked.
The U.S. has moved to bring Iran's oil exports to zero to try and pressure Tehran.
Iran has responded by beginning to breach limits put on its nuclear activities in a 2015 deal with world powers.