Prime Minister Theresa May has chaired an emergency Cobra meeting after a British-flagged oil tanker was seized by Iranian authorities.
The UK-registered Stena Impero tanker was detained by the Iranian Revolutionary Guard in the Strait of Hormuz on Friday, July 19.
Former Foreign Secretary Jack Straw told talkRADIO it was a “tit-for-tat” reaction after Britain seized an Iranian tanker earlier this month.
On July 4, British Royal Marines and authorities in Gibraltar detained the Iranian-flagged Grace 1, which was believed to be in breach of EU sanctions.
Iran's revolutionary guard warned a British oil tanker could be seized in retaliation.
Here is a timeline of what has happened since:
The British-flagged Stena Impero was seized by the Iranian Revolutionary Guard in the Strait of Hormuz.
An Iranian news agency said it was because the ship "violated international maritime rules".
A second oil tanker, the Liberia-flagged Mesdar, managed Norbulk Shipping UK, also appeared to veer off-course towards the Iranian coast.
It was boarded by armed guards but the crew were left "safe and well" and allowed to continue their voyage.
July 20 - 21
Meetings were held by the government’s emergency committee Cobra over the weekend.
Jeremy Hunt said the seizure of the Stena Impero raised "very serious questions" about the security of British and international shipping in the region.
Theresa May was not present at the meetings but was kept informed of developments.
Meanwhile, an audio recording of an exchange between Iranian authorities and HMS Montrose in the moments before the Stena Impero was seized, emerged.
In the radio recording, the Iranian vessel can be heard saying: "If you obey, you will be safe. Alter your course immediately. I want to inspect the ship for security reasons."
HMS Montrose replied: "You must not impair, impede, obstruct or hamper the passage of the Stena Impero. Please confirm that you are not intending to violate international law by attempting to board."
Theresa May returned from her consituency in Maidenhead to chair an emergency Cobra meeting.
Foreign Secretary Jeremy Hunt told MPs the seizure was an act of "state piracy".
Pictures were also released by Iranian state media of the 23-strong Stena Impero crew.
It appears to show cooks preparing meals, and the crew members being spoken to by an Iranian official onboard the tanker.
Britain has demanded the tanker is released.