The war of words escalated sharply today over British sailors captured by Iran in the Gulf, with Tehran putting off freeing a female prisoner and London calling her treatment "outrageous and cruel".
Britain launched a diplomatic offensive, drafting a strongly-worded condemnation of Iran for the UN Security Council and seeking to persuade European Union members to join it in cutting back diplomatic relations with Tehran.
Prime Minister Tony Blair said he was disgusted by Iran's treatment of the prisoners, adding he would not enter "tit-for-tat" negotiations to secure their release.
Mr Blair told ITV television: "What I'm afraid we can't do is end up in negotiation over hostages ... This is not a situation that can be resolved by anything other than the unconditional release of all our people."
Iran has shown the prisoners on television, and today distributed a second letter purportedly from the only female captive, Faye Turney, confessing to entering Iranian waters.
Both letters were in stilted English, with unusual phrases that linguistic experts said appeared to have been translated from Farsi into English.
The letter said: "Unfortunately during the course of our mission we entered into Iranian waters. Even through our wrongdoing, they have still treated us well and humanely, which I am and always will be eternally grateful,"
The letter also called for British forces to withdraw from Iraq.
"We have not seen this letter but we have grave concerns about the circumstances in which it was prepared and issued. This blatant attempt to use Leading Seaman Turney for propaganda purposes is outrageous and cruel," British Foreign Secretary Margaret Beckett said.
Iran had promised yesterday to free Seaman Turney soon. But today Iranian military commander Alireza Afshar said her release had been "suspended".
"The wrong behaviour of those who live in London caused the suspension," he said. Britain must apologise for entering Iran's waters and promise it would not happen again, he added.
But Iranian state television reported that President Mahmoud Ahmadinejad would consider a Turkish request to free her.
The six-day-old dispute has stoked Middle East tensions, already heightened over concerns about Iran's nuclear ambitions.
Britain says satellite data proves its 15 sailors and marines were seized last week in Iraqi waters. But Iran responded today by showing video of the capture and charts it says shows it took place in Iranian waters.