"The British charge d'affaires in Tehran ... had confirmed the unauthorised and unintentional straying of the boats to Iranian waters," Iranian Foreign Ministry spokesman Hamid Reza Asefi said on Thursday.
Britain said on Wednesday Iranian Revolutionary Guards had forced eight British navy personnel into Iranian waters while the men were operating inside Iraqi territory on the Shatt al-Arab waterway along the Iran-Iraq border.
It was the latest diplomatic friction over the incident which occurred at a time when British relations with Iran had already soured over London's criticism of Tehran's alleged failure to cooperate with UN nuclear inspectors.
Iran held the British crewmen for three nights before handing them over to British diplomats. Tehran said they had mistakenly veered off course.
The crewmen now say they were
operating inside the Iraqi border
In a written statement to the British parliament on Wednesday, Defence Secretary Geoff Hoon said: "The initial assessment ... was that these service personnel could have strayed into Iranian waters by mistake."
"In recent more detailed debriefing, the crews have said that they were operating inside the Iraqi border and were forcibly escorted into Iranian territorial waters."
The British prime minister's office said on Thursday the eight British naval personnel "had no intention to go into Iranian waters".
"The important thing was to ensure the safe return of those involved, and that was done. We don't expect a recurrence of such an event," Prime Minister Tony Blair's official spokesman told reporters.
Unlike the United States, Britain has pursued a policy of engaging Iran in recent years. London has said it will continue that policy despite the arrest of the eight British servicemen.
"We don't expect a recurrence of such
Tony Blair's office
As Britain's main priority was the immediate release of its navy personnel, London acted accordingly, a Western diplomat in Tehran said.
A delegation of British diplomats from Tehran travelled to the southwestern province of Khuzestan to negotiate the release of the eight servicemen and flew with them to the capital from the Gulf area where the men were detained.
"The delegation was not allowed to talk to the crewmen in private ... now after a proper debriefing, this may have been a little too charitable," the diplomat added.