Britain has called Iran's capture of the Stena Impero in the Gulf on Friday a "hostile act" and rejected Tehran's explanation that it seized the vessel because it had been involved in an accident.

The "UK government should contain those domestic political forces who want to escalate existing tension between Iran and the UK well beyond the issue of ships. This is quite dangerous and unwise at a sensitive time in the region," Iran's envoy to Britain Hamid Baeidinejad said on Twitter.

"Iran however is firm and ready for different scenarios," he said.

A day earlier British foreign minister Jeremy Hunt said Tehran's actions showed "worrying signs Iran may be choosing a dangerous path of illegal and destabilising behaviour after Gibraltar's legal detention of oil bound for Syria."

The crew of the tanker seized by Iran's Revolutionary Guards are all safe, the head of the Ports and Maritime Organisation in Hormozgan Province told state TV on Sunday.

"All 23 crew members aboard the ship are safe and in good health in Bandar Abbas port," Allahmorad Afifipour said.

Afifipour said the seized tanker "risked maritime safety" in the Strait of Hormuz, through which almost a fifth of the world's annual oil consumption passes.

"We are required by regulations to investigate the issue ... the duration of the investigation depends on the level of cooperation by the involved parties," said Afifipour.

The seizure has heightened tension between Iran and Britain, which is a party to Iran's 2015 multinational nuclear deal. The Daily Telegraph newspaper reported on Saturday that London was planning to target Iran with sanctions in the aftermath of the tanker seizure.

In a letter to the UN Security Council, Britain said the tanker was approached by Iranian forces in Omani territorial waters where it was exercising its lawful right of passage, and that the action "constitutes illegal interference."

Stena Bulk, the vessel's Sweden-based owners, said it is preparing a formal request to visit the crew, who are from India, Latvia, the Philippines and Russia. India has called on Iran to release the 18 Indian crew members.

Tehran for weeks has vowed to retaliate for the seizure by Royal Marines of the tanker Grace 1 carrying Iranian oil near Gibraltar on July 4 which was suspected of violating sanctions on Syria.

US President Donald Trump pulled the US out of the nuclear agreement with Iran last year and reimposed sanctions on Iran's oil and banking sectors.

Iran has repeated threatened to close the Strait of Hormuz if it cannot export its oil because of the sanctions but cannot legally do so as part of the waterway is in Oman's territorial waters.

Oman has urged Iran to release the Stena Impero, calling on all parties to exercise restraint and resolve differences diplomatically, state broadcaster Oman TV News reported on Sunday.

Australian Associated Press