Faye Turney, 26, left, the only woman amongst the British navy personnel seized by Iran, and an unidentified sailor eat a meal, in this image made from television, in footage broadcast by Al-Alam, an Arabic-language, Iranian state-run television station, in Tehran, Wednesday March 28, 2007. [AP]

UNITED NATIONS - The U.N. Security Council expressed "grave concern" Thursday over Iran's seizure of 15 British sailors and marines and called for an early resolution of the escalating dispute, but Iran's chief international negotiator suggested the captives might be put on trial.

The council's statement wasn't as tough as Britain had hoped, though, and the divide seemed to deepen.

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As the standoff drove world oil prices to new six-month highs, Turkey, NATO's only Muslim member, reportedly sought to calm tensions by urging Iran to let a Turkish diplomat meet with the detainees and to free the lone woman among the Britons.

Tensions had seemed to be cooling a day earlier, but after Iran offended leaders by airing a video of the prisoners and Britain touched a nerve in Tehran by seeking U.N. help, positions hardened even more Thursday.

Iran retreated from a pledge by Iranian Foreign Minister Mottaki that the female sailor, Faye Turney, would be released soon. Mottaki then repeated that the matter could be resolved if Britain admitted its sailors mistakenly entered Iranian territorial waters last Friday.

Britain's Foreign Office insisted again that the sailors and marines were seized in an Iraqi-controlled area while searching merchant ships under a U.N. mandate and said no admission of error would be made.

With Britain taking its case to the United Nations, Ali Larijani, the top Iranian negotiator in all his country's foreign dealings, went on Iranian state radio to issue a warning.

He said that if Britain continued its current approach, "this case may face a legal path" -- a clear reference to Iran prosecuting the sailors and marines in court. "British leaders have miscalculated this issue," he said.

Gen. Ali Reza Afshar, Iran's military chief, blamed the backtracking on releasing the British woman on "wrong behavior" by her government. "The release of a female British soldier has been suspended," the semiofficial Iranian news agency Mehr said.

The Security Council's statement was a watered-down version of a stronger draft sought by Britain to "deplore" Iranian actions and urge the immediate release of the prisoners, primarily because Russia and South Africa opposed putting blame on the Tehran regime, diplomats said.

Russia also objected to the council adopting Britain's position that its sailors were operating in Iraqi waters when they were captured, the diplomats said, speaking on condition of anonymity.

With agreement required from all 15 members for a statement's wording, the parties spent more than four hours in private talks before emerging with wording softer than had been sought by Britain, which is also known as the United Kingdom.

"Members of the Security Council expressed grave concern at the capture by the Revolutionary Guard and the continuing detention by the government of Iran of 15 United Kingdom naval personnel and appealed to the government of Iran to allow consular access in terms of the relevant international laws," the statement said.

"Members of the Security Council support calls including by the secretary-general in his March 29 meeting with the Iranian foreign minister for an early resolution of this problem including the release of the 15 U.K. personnel."

South African Ambassador Dumisani Kumalo said negotiations were needed to ensure the statement focused on the agreed facts. "There is no political twisting of anything that happened," he said.

British Ambassador Emyr Jones Parry expressed satisfaction with the statement and said he hoped it would send "the right message" to the Iranian government that it should provide immediate access to the prisoners and bring their prompt release.

Earlier, Iranian state television reported what was believed to be Ahmadinejad's first comment on the standoff, saying he accused Britain of using propaganda rather than trying to solve the matter quietly through diplomatic channels.

Iran's state TV also said Turkish Prime Minister Recep Tayyip had contacted Ahmadinejad seeking permission for a Turkish diplomat to meet with the seized Britons and urging the release of Turney, the female sailor.

Erdogan's move was seen as a possible opening to mediation in the faceoff because Turkey is one of the few countries that has good relations with both Iran and the West.

The report said Ahmadinejad promised that Erdogan's appeal would be studied, but also told the Turkish leader that the detention case had entered a legal investigation phase.

State television also broadcast a video it said showed show the operation that seized the British sailors and marines. In the clip, a helicopter hovers above inflatable boats in choppy seas, then the Royal Navy crews are seen seated in an Iranian vessel.

The video came a day after Iran broadcast a longer video showing the Britons in captivity. That video included a segment showing Turney saying her team had "trespassed" in Iranian waters.

British Foreign Secretary Margaret Beckett condemned Iran's use of Turney for what she called "propaganda purposes," calling it "outrageous and cruel."

The Iranians released a letter Wednesday purportedly written by Turney to her family saying the British sailors were in Iranian waters. And the video aired Thursday showed another letter supposedly by Turney to Britain's Parliament calling for British troops to leave Iraq.

"I ask the representatives of the House of Commons, after the government promised that this kind of incident wouldn't happen again, why did they let this occur, and why has the government not been questioned over this," the letter read. "Isn't it time to start withdrawing our forces from Iraq and let them determine their own future?"

Some experts raised questions about that letter, saying its wording hinted it was first composed in Farsi and then translated into English.

"It's obviously been dictated to her," said Nadim Shehadi, an expert on Iran at the Chatham House think tank in London. "There's no way she would phrase it like that."

Beckett said there were "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," Beckett said.

A spokesman for Prime Minister Tony Blair said Britain wanted to resolve the crisis quickly and without having a "confrontation over this."

"We are not seeking to put Iran in a corner. We are simply saying, 'Please release the personnel who should not have been seized in the first place,'" said the spokesman, speaking on condition of anonymity in line with government policy.

But in a briefing to reporters, the spokesman said British officials had been angered by Tehran's decision to show video of the captives.

"Nobody should be put in that position. It is an impossible position to be put in," he said. "It is wrong. It is wrong in terms of the usual conventions that cover this. It is wrong in terms of basic humanity."