Lessons learned: Iran's release of British prisoners

That was the approach in 2004, when six British sailors and marines were seized in a similar part of the Persian Gulf, Britain took a face-saving approach, quietly admitting that its personnel may have strayed across the border by mistake.

This time around, however, there was intense discussion in London about how hard-line Britain's approach should be, says Dr. Ansari. But in the end, those advocating for diplomacy – in both Iran and Britain – triumphed, he says. "I think the battle was won on both sides [Iranian and British] by those saying 'We have to take this with firm resolve, but with a diplomatic approach.'

Hollis at Chatham House, adds: "The ingredients for a diplomatic solution have always been present, but it took a senior figure in Tehran to clarify that that was also what they were looking for, and how to proceed."

But other analysts were more critical of the resolution.

"[The Iranians] have pulled off a significant propaganda coup," says Major (ret.) Charles Heyman, a British defense expert. "There's a subtext to this – that we [the Iranians] are the innocent party, and we are behaving as rational and decent people. What they're really saying is, 'We're a joined up member of the international community whether you like it or not.' It's very difficult for us to respond to it other than by saying thank you – very difficult."

Ahmadinejad's announcement came after Iran's state media reported that an Iranian envoy would be allowed to meet five Iranians detained by US forces in northern Iraq. Another Iranian diplomat, separately seized two months ago by uniformed gunmen in Iraq, was released and returned Tuesday to Tehran. But Ahmadinejad said there was no connection to the release of the Britons.

"If we had wanted to exchange Jalal Sharafi with the rest [the Britons] we would have exchanged him for 100,000 [people]. But we pardoned them," he said, adding the decision was "based on humanitarian considerations."

After his announcement, crude oil prices slipped. Oil futures had surged 7 percent, to above $64 a barrel, since the sailors were taken hostage on March 23.

Ahmadinejad said the British government had sent a letter to the Iranian Foreign Ministry pledging that entering Iranian waters "will not happen again."

In his press conference, Ahmadinejad said, "On the occasion of the birthday of the great prophet [Muhammad] ... and for the occasion of the passing of Christ, I say the Islamic Republic government and the Iranian people – with all powers and legal right to put the soldiers on trial – forgave those 15," he said, referring to the Muslim prophet's birthday on March 30 and the Easter holiday. "This pardon is a gift to the British people," he said.

The family of British Royal Marine Adam Sperry hailed the announcement as "the best present imaginable".

"The one thing I wanted was Adam's safe return to his family for Easter," Mr. Sperry's uncle, Ray Cooper, told the Associated Press. "Whoever has been in the right or wrong, the whole thing has been a political mess, so let's just get them home. It's great."

• Christa Case contributed reporting from Boston. Material from wire services was also used in this report.

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