Iran: The release of the 15 Britons was a "gift" to the British people to celebrate the birth of the prophet Muhammad and Easter, according to Iran's president Mahmoud Ahmadinejad.
It also came two hours after an American general revealed the US might allow Iranian diplomats to visit five countrymen arrested in Iraq three months ago.
The timing has fuelled speculation of a deal to free the British sailors and marines seized by Iranian Revolutionary Guards.
In a further coincidence, yesterday's unexpected announcement came a day after the mysterious release of another Iranian diplomat, Jalal Sharafi, kidnapped in Baghdad at the beginning of the year by gunmen in Iraqi government uniforms.
The 13-day crisis was enveloped in a fog of secret diplomacy and informal talks. Syria claims to have played a leading role in persuading Iran of the foolishness in detaining the Britons any longer.Iran's decision may have been the culmination of many reasons, but observers say Tehran must have been convinced it was in its interests to give up its bargaining chips.
The existence of a deal was denied by all involved. US president George Bush insisted there would be no "quid pro quo". British officials said they had Iranian assurances a prisoner swap was not on the agenda and Mr Ahmadinejad was adamant the release was for "humanitarian reasons".
Iraqi foreign minister Hoshyar Zebari, who appears to have played a critical go-between role, added his voice to the chorus of denial. "The British media are linking it as if it is part of bargain with Iran to release the British sailors and marines. It has no connection whatsoever," he told the Guardian yesterday.
Mr Zebari said he had asked the US military to grant consular access to the Iranian diplomats in a bid to "ease the atmosphere" between Iran and the US at the time of last month's Baghdad security conference. US military spokesman Maj Gen William Caldwell said authorities were considering the request for access.
A source close to the Revolutionary Guards gave a different account. The fate of the diplomats was not a motive for the capture, he said, but it did become a negotiating point after the event.
He provided the first comprehensive Iranian version of events on March 23rd when the 15 Britons were captured by Revolutionary Guard sailors on the shallow seas of the northern Gulf. Not only had the British patrol strayed into Iranian waters, he claimed, but it was at least the fourth incursion in three months.
The US refusal to exclude the use of military force against Iran to stop its nuclear programme, together with a series of separatist attacks in Iran's border regions, had put the Revolutionary Guard on alert for incursions.
The investigation into the incident would have run its course and the Britons would have been released, but the affair was complicated by prime minister Tony Blair's decision to take the matter to the UN security council last Wednesday, he added.
The return of Mr Sharafi to Iran on Tuesday and the prospect of access to the five diplomats strengthened the hand of Mr Ahmadinejad, according to Issa Saharkhiz, a political analyst.
The Britons' televised "confessions" have served an internal political purpose - convincing a sceptical public that Iran is threatened by a determined enemy.