The UK and Iran have summoned each other's diplomats in a row over last week's deadly attack on an oil tanker off the coast of Oman.
The UK, US and Israel blame Iran for the attack, in which two crew members - a Briton and a Romanian - were killed.
Tensions are high between Israel and Iran and each has regularly accused the other of targeting shipping in the region.
Iran dismissed accusations it was behind the latest attack as baseless.
On Monday, the UK summoned Iran's ambassador over what the British government called the "unlawful attack".
British Prime Minister Boris Johnson said Iran should "face up to the consequences of what they've done" calling the incident an "an unacceptable and outrageous attack on commercial shipping".