The UK has said it is deeply concerned over Iran's seizure of a British-flagged tanker, comprising 18 Indians in its 23-member crew, in the Gulf and warned Tehran against choosing a "dangerous path of illegal and destabilising behaviour."
British-flagged tanker Stena Impero was seized on Friday by the Iranian Revolutionary Guard in the Strait of Hormuz amid fresh escalation of tensions in the Gulf.
Iran's state-run IRNA news agency said the tanker was seized after it collided with a fishing boat and failed to respond to calls from the smaller craft.
It said there no reported injuries among the crew members, which also includes five Russians, a Latvian and a Filipino.
UK foreign secretary Jeremy Hunt termed the seizure as "completely unacceptable" and stressed that "freedom of navigation must be maintained".
The incident comes days after an Iranian oil supertanker, Grace 1, was seized off the Spanish coast earlier this month by Iran and four of its Indian crew members were arrested by the the Royal Gibraltar Police (RGP).
Our reaction will be considered but robust. We have been trying to find a way to resolve Grace 1 issue but WILL ensure the safety of our shipping, Hunt said in a statement on Twitter on Saturday.
Yesterday's action in Gulf shows worrying signs Iran may be choosing a dangerous path of illegal and destabilising behaviour after Gibraltar's LEGAL detention of oil bound for Syria, he added.
The British-flagged Stena Impero was surrounded by four vessels and a helicopter before heading into Iranian waters, Hunt said.
The Stena Impero's owners say they have been unable to contact the ship.
They said that the vessel owners was fully complying with regulations and it was in international waters when it was approached.
A second British-owned Liberian-flagged tanker, the MV Mesdar, was also boarded by armed guards but was released.
"We are not looking at military options. We are looking at a diplomatic way to resolve this situation," Hunt said soon after the incident on Friday.
He said he was "deeply concerned" by the seizure of two naval vessels by Iranian authorities in the Strait of Hormuz.
Meanwhile, the Indian crew members from the Grace 1 vessel remain on bail.
The local force for Gibraltar, a British Overseas Territory, said the investigation is ongoing and the oil tanker Grace 1 remains in detention.
The latest developments come amid a deterioration in relations between Iran, the UK and the US. Tensions between the US and Iran have risen sharply since April, when the US tightened sanctions it had reimposed on Iran after unilaterally withdrawing from the 2015 nuclear deal.