oil tanker
The UK must be responsible for the safety of its own ships in the Gulf, the US secretary of state, Mike Pompeo, has said.

His remarks reflect unresolved tensions between Britain and the US over Donald Trump's plans for a US-led military convoy to protect international shipping operating off the Iranian coast.

Speaking on Fox News, Pompeo said: "The responsibility in the first instance falls to the United Kingdom to take care of their ships. The US has a responsibility to do its part."

British ministers discussed the issue at a Cobra emergency meeting that largely focused on how to respond to the Iranian capture on Friday of the British-flagged Stena Impero. The ship, crewed largely by Indian nationals, is being held in the Iranian port of Bandar Abbas. All crew members are in good health and still onboard, the Iran embassy in India said on Monday.

The detention comes at a time of high tension in the region, with US, British and Iranian forces facing off at sea.

The UK foreign secretary, Jeremy Hunt, spoke to his German and French counterparts on Sunday to urge them to recognise the need to internationalise the maritime security operation in the Gulf. A multinational task force already exists, and it is not clear what the US believes its proposed Operation Sentinel will add.

A spokesman for the prime minister, Theresa May, said: "We already work closely with international partners to ensure a co-ordinated effort to defend freedom of navigation ... The high volume of ships moving through the Strait of Hormuz - up to 30 ships covering more than 100 nautical miles - makes it impossible to escort vessels individually".

About a fifth of the world's oil passes through the Strait of Hormuz, the busiest shipping lane in the world for crude tankers, and it is less than 25 miles (40km) wide at its narrowest point. Tensions in the Gulf had already affected oil trading, and Friday's tanker seizures caused prices to rise.

Britain has concerns that a US-led maritime security operation may have a different emphasis since Trump wants Europeans to join the US in pulling out of the nuclear deal signed in 2015.

The UK has already advised all British-flagged ships not to enter the Strait of Hormuz until the crisis is resolved. There are eight British-flagged ships in the region at present.

In a statement to MPs on Monday, Hunt will vigorously defend the British decision to seize an Iranian tanker off Gibraltar on 4 July, insisting Britain - in co-operation with the US - had established that the ship entered British waters and was bound for Syria in breach of EU sanctions.

Iran says it is not party to EU sanctions on Syria, and points out that no ship previously heading for Syria has been impounded in this way. Iran claims the UK has in effect ended up supporting the US efforts to impose an Iranian oil export ban, a measure that the UK formally opposes as a supporter of the 2015 nuclear deal.

The UK Foreign Office is aware that the advent of the pro-US Boris Johnson as prime minister may see a change in UK policy towards the deal, or at least to the idea of a US-led maritime security convoy, but at present diplomats remain committed to the long-established European policy of protecting the deal.

There is an urgency about the security of British ships, since one option is for British-flagged ships to be reflagged to avoid them becoming a target of the Iranians, something that would deal a blow to the British shipping industry.

There are about 4,500 ships registered with Britain or its overseas territories.

Lord Lamont, the former chancellor, and head of the British-Iranian chamber of commerce, said Britain must resist the temptation to get drawn closer to the US. "More armed escorts are not going to solve the situation," he said. "The risk of a loss of life is very high and then you will get a proper shooting war." The Iranians will have seen the capture of the Stena as offsetting the interdiction of the Iranian tanker, he added.

Pompeo also dismissed Iran's announcement that it had captured 17 spies working for the US Central Intelligence Agency and sentenced some to death.

Iran made the announcement in state media, saying the alleged spies had been arrested in the 12 months to March 2019. Such announcements are not unusual in Iran, but the timing has raised concerns that Tehran is hardening its position in its standoff with western powers. "The Iranian regime has a long history of lying ... I would take with a significant grain of salt any Iranian assertion about actions that they've taken," Pompeo said.

Donald Trump likewise tweeted that the Iranian claim was "totally false".