LONDON - Britain was seriously considering on Friday a note from Iran about 15 British sailors and marines detained in the Gulf after London failed to secure tough international condemnation of the seizure last week.

Faye Turney, the only woman crew member of the 15 British sailors and marines detained at sea last week, speaks during an interview on Iranian television March 28, 2007. [Reuters]

Iran's message, the first written communication from Tehran to Britain since the sailors were seized, appeared to resemble a statement used to resolve a similar standoff in 2004 when Iran seized eight British servicemen and held them for three days.

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A British Foreign Office spokeswoman said Britain was preparing a response to the note over a crisis which has helped send oil prices to the highest levels for almost seven months.

"...We are giving the message serious consideration, and will soon respond formally to the Iranian government," she said, without giving details.

Iran's IRNA news agency said the Iranian Foreign Ministry had sent a message to the British embassy in Tehran asking for "necessary guarantees that violations against Iranian waters would not be repeated."

Britain and Iran are at odds over whether the 15 Britons were in Iranian or Iraqi waters when captured carrying out patrols authorized by the United Nations and Iraq's government.

London says satellite data prove last Friday's seizure happened in Iraqi waters, but Tehran has video footage and charts it says show the event took place in Iranian waters.

Britain has sought international support for its position, with mixed results.

The UN Security Council on Thursday agreed a watered down statement expressing "grave concern" at the situation and supporting calls for the crew's release.

Britain, which had sought a tougher statement, plans to urge the European Union to help isolate Iran at a two-day meeting of EU ministers starting on Friday.

French Foreign Minister Philippe Douste-Blazy condemned on Friday the detention of British sailors by Iran but indicated that France was not ready to support calls by London to freeze ties with Iran over the issue.

Britain, which has frozen all diplomatic business with Tehran apart from discussions over the prisoners, wants fellow EU nations to follow its lead and adopt tough measures, British government sources have said.

"At the moment we are totally behind the British," Douste-Blazy told RTL radio. Asked repeatedly if France would freeze ties with Iran, the minister said: "Today there has been no freezing (of relations)."

Asked what would happen if Tehran refused to release the sailors immediately, he said: "There will be a new meeting at the UN Security Council to decide what to do."

"We need to put very strong pressure on the Iranians. We cannot accept that ... they capture and detain these British sailors," he said.

Ratcheting up emotions, Iran on Thursday released a second letter purportedly by the only female member of the crew, Faye Turney, in which she again said her patrol had "entered into Iranian waters."

Britain reacted angrily to what it said was blatant propaganda, labeling the note's release "outrageous and cruel."

Both letters from Turney, 26, a mother and wife from southwest England, were in stilted English, leading some linguistic experts to suggest the text may have been written originally in Farsi and translated into English.