British Prime Minister Tony Blair warned Iran on Tuesday that the standoff over the capture of 15 sailors would enter a "different phase" if diplomatic efforts to secure their release failed.
Blair said all efforts were on securing their swift return through diplomacy, but warned Britain cannot allow its service personnel to be seized with "no justification whatever".
"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," he told GMTV television.
"I hope we manage to get them to realise they have to release them. If not, then this will move into a different phase."