LONDON, March 23: The Iranian navy has seized up to 15 British sailors, the UK’s Ministry of Defence confirmed on Friday, sparking a diplomatic standoff between Tehran and London.

Iran's ambassador to the UK was immediately summoned to the foreign office for what the foreign secretary, Margaret Beckett, described as a “brisk” meeting. He was “left in no doubt” that Britain expected the immediate return of the sailors and their boats, she said.

However, Iran’s government responded by summoning the British charge d'affaires to Tehran to protest at the illegal entry of British naval personnel into Iranian waters. “The Iranian foreign ministry has seriously objected following the illegal entry of British naval military forces into our country's waters,” state television reported.

According to the ministry of defence, the Royal Navy and Royal Marines personnel were taken after they had boarded a dhow in Iraqi waters during a patrol in the Shatt al-Arab waterway at 10.30am local time.

As the sailors searched the fishing boat for signs of possible smuggling activity, Iranian boats approached it and captured them at gunpoint. The men, who had approached the dhow in two inflatable boats from the frigate HMS Cornwall, were taken to an Iranian naval base.

“The boarding party had completed a successful inspection of a merchant ship when they and their two boats were surrounded and escorted by Iranian vessels into Iranian territorial waters,” a spokesman for the MoD said.

Mrs Beckett said the government had been “disturbed” to hear of the incident. The Iranian ambassador was called to see the foreign office permanent secretary, Sir Peter Ricketts, and the matter was also raised with officials in Tehran, she said in a statement. The commanding officer of HMS Cornwall, Commodore Nick Lambert, said his “immediate concern” was for the welfare of his crew. “I have got 15 sailors and marines who have been arrested by the Iranians,” he told the BBC.

He said the 15 men were all believed to be safe, adding: “We know there was no fighting, there was no engagement of weapons or anything like that — it was entirely peaceful. “We have been assured from the scant communications that we have had with the Iranians at the tactical level that 15 people are safely in their hands.”

He said the incident appeared to be the result of a “misunderstanding” which could be quickly resolved.

Commodore Kevin Aandahl, of the US Navy’s Fifth Fleet — which operates jointly with the British forces off the coast of Iraq — said the UK crew members had been intercepted by several larger patrol boats. The boats were operated by Iranian sailors belonging to the Iranian Revolutionary Guard Corps Navy, a radical force operating separately from the country’s usual navy.

Iran has captured British service personnel on the Shatt al-waterway before. Eight crew members from the three boats — sailors and marines who were part of a British team training Iraqi river police — were held by the Iranian authorities in May 2004. —Dawn/ The Guardian News Service