March 30 (Bloomberg) -- European Union foreign ministers pressed Iran to release 15 captive British sailors and marines, calling the arrest a ``big mistake'' that could do further damage to Iran's international standing.

``The European Union repeats its call for the immediate and unconditional release of the British Royal Naval personnel,'' the ministers said in a statement after a meeting in Bremen, Germany today.

Iran's seizure of the U.K. military personnel on March 23 in what it said were Iranian waters adds a new complication to diplomatic efforts to persuade the Islamic Republic government to scale back its nuclear program.

The United Nations Security Council yesterday expressed ``grave concern'' and called for an ``early'' end to the dispute, without demanding the immediate release of the captives. Britain says the troop boats were in Iraqi waters at the time.

Iran's move was ``a big mistake,'' EU foreign policy chief Javier Solana told reporters. ``They should release the soldiers immediately.''

`All Evidence'

The EU said ``all evidence clearly indicates'' that the U.K. boats were in Iraqi waters. The EU called on Iran to disclose where the captives are being held and allow U.K. diplomats to see them. ``Should the U.K. citizens not be released in the near future, the EU will decide on appropriate measures,'' the EU statement said.

The international pressure may be starting to have an impact. In a letter delivered to the U.K. embassy in Tehran late yesterday, Iran dropped its demand for an apology while seeking assurance that the Britain ``guarantee to avoid the recurrence of such acts.'' The letter was reprinted today by the official news agency.

In Washington, a spokeswoman for President George W. Bush said the U.S. supports British Prime Minister Tony Blair. ``We believe that Iran should make the decisions to immediately and unconditionally release the 15 British soldiers being held,'' spokeswoman Dana Perino told reporters at the White House. ``We believe, as Tony Blair has said, that the British soldiers were in Iraqi waters and that they need to be returned immediately.''

The only woman among the captives, Faye Turney, remained in custody today, two days after the Iranian government said it would let her go.

TV Broadcast

Iranian television today showed a second U.K. naval crew member who it said confessed to illegally entering Iran's waters, after the Foreign Ministry in Tehran demanded a ``guarantee'' that there won't be further border violations.

U.K. Foreign Secretary Margaret Beckett said the international community is lining up against Iran.

``We've got a clear indication from the UN that people would like to see this peacefully resolved and as quickly as possible,'' Beckett said.

A day after the arrests, the Security Council voted unanimously on a second resolution condemning Iran's nuclear program and stiffening the sanctions that were imposed in December.

To contact the reporters on this story: James G. Neuger in Bremen at jneuger@bloomberg.net; Mark Deen in Bremen at markdeen@bloomberg.net.

Last Updated: March 30, 2007 17:43 EDT