Behind the Denials, A De Facto Hostage Exchange By PATRICK COCKBURN

The stand-off over the 15 British sailors and marines captured by Iran ended with a de facto prisoner exchange, despite denials by Britain and Iran that a swap was intended.

The first sign of a breakthrough the day before yesterday was the release of Jalal Sharafi, an Iranian diplomat abducted from the streets of Baghdad two months ago, whom Iran claimed had been seized by Iraqi commandos controlled by the US. At the same time, an Iraqi Foreign Ministry official said the Iraqi government was "intensively" seeking the release of five Iranian officials captured in a US helicopter raid on a long-established Iranian liaison office in the Kurdish capital of Arbil in January.

The seizure of the sailors and marines was the latest episode in a series of tit-for-tat confrontations between the US and Iran which began when the US tried to seize senior Iranian intelligence officials on an official visit to Arbil on January 11. The raid failed and only succeeded in detaining five Iranian officials at the liaison office, which has now been officially recognized as a consular office.

Senior Kurdish officials told me that the real US targets were Mohammed Jafari, the powerful deputy head of the Supreme National Security Council, and General Minojahar Frouzanda, the head of intelligence of the Iranian Revolutionary Guards. They had visited President Jalal Talabani of Iraq at Dokan near Sulaimaniyah and then gone on to Arbil where they saw Massoud Barzani, president of the Kurdistan regional government, at his headquarters outside the city.

The Arbil raid came a few hours after an aggressive address to the nation by President George Bush, in which he denounced Iran as America's great enemy in Iraq. It has been followed by a series of tit-for-tat incidents such as the attempted abduction of five US soldiers in a highly sophisticated attack near the holy city of Kerbala, south of Baghdad, in which the assailants first tried to take prisoner the US soldiers but later killed them. The US blamed the episode on Iraqi Shias acting as proxies for Iran.

The release of Mr Sharafi turned out to be thed trigger for release of the British hostages. He was seized in mysterious circumstances on February 4 by uniformed men. Iran and some Shia politicians in Baghdad said they were from the 36th Commando Unit of the Iraqi Army that was, in practice, controlled by the US. Mr Sharafi has now returned to Tehran. The US denies any role in his disappearance. At the same time, immediately after the Arbil raid, the US Secretary of State, Condoleezza Rice, revealed that President Bush had approved a policy of raiding Iranian targets on Iraqi soil.

Neither Mr Sharafi, a second secretary at the embassy, nor the five Iranian officials seized in Arbil seem to have been important figures. Mr Sharafi was involved in plans to open a branch of the Iranian national bank in Baghdad. One of the captives from Arbil was described by the US as a senior officer of the Quds Force, an elite unit of Iran's Revolutionary Guards.

American and British claims that there was no connection between the capture of Iranian officials on January 11 and the seizure of the British sailors and marines was undermined on April 3 when the Iraqi Foreign Ministry official said his government was also working "intensively" for the release of those five other Iranians to "help in the release of the British sailors and marines".

In Washington, President Bush signalled the same: "I also strongly support the Prime Minister's declaration that there should be no quid pro quos when it comes to the hostages," he said.

Patrick Cockburn is the author of 'The Occupation: War, resistance and daily life in Iraq', a finalist for the National Book Critics' Circle Award for best non-fiction book of 2006.