Britain's relations with Iran will move into "a different phase" unless Tehran quickly releases 15 British sailors and Marines taken hostage last week, Tony Blair said today.

The Prime Minister gave the warning while insisting that diplomatic channels remained the preferred route to secure the release of the personnel, who were seized in the disputed Shatt al Arab waterway which divides Iran and Iraq on Friday.

Asked whether there was any news on the eight sailors and seven Marines this morning, Mr Blair told GMTV: "No, there isn’t, but let me just say our first concern is for their welfare and to get them released as quickly as possible.

"What we are trying to do at the moment is to pursue this through the diplomatic channels and make the Iranian government understand these people have to be released and that there is absolutely no justification whatever for holding them. I hope we manage to get them to realise they have to release them. If not, then this will move into a different phase."

The Prime Minister's spokesman later explained that by saying "different phase", Mr Blair meant that Britain might explore alternative means of negotiating with Iran, such as making public the exact co-ordinates of the incident last Friday, which would indicate that it took place in Iraq waters.

Last night relatives of the only woman among those taken hostage, Leading Seaman Faye Turney, spoke of their distress at her capture. Today a photograph of Ms Turney, taken six years ago when she was serving with the Royal Navy in Sierra Leone, was released.

In a statement released by the Ministry of Defence, Ms Turney's family said: "While we understand the media interest in the ongoing incident involving Faye, this remains a very distressing time for us and our family. We are grateful for the support shown to us by all personnel involved and appreciate it, but would request that our privacy is respected."

This evening, a second of the hostages was named as Paul Barton, 21, from the Marshside area of Southport in Merseyside, who it is believed only completed his training with the Royal Marines last year.

Iran stated once again today that the sailors and Marines from HMS Cornwall were safe and well but refused to confirm reports that they had been brought to the capital.

"They are in completely good health. Rest assured that they have been treated with humanitarian and moral behavior," Mohammad Ali Hosseini, a spokesman for the Foreign Ministry, told the Associated Press.

Mr Hosseini said that Ms Turney was being held apart from the others to give her privacy. "Definitely all ethics have been observed," he said.

He added that the personnel were being interrogated as to whether they entered Iranian waters deliberately or not, suggesting a possible way out of the impasse. Until now, Iran has threatened to put the sailors and Marines on trial for spying.

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