British Foreign Secretary Margaret Beckett on Tuesday urged caution over expecting a swift resolution to the crisis involving 15 detained naval personnel, hours after British Prime Minister Tony Blair said the next 48-hours would be critical to quickly resolving the standoff.

"We should be cautious in thinking we will see a swift conclusion," Beckett said. "Diplomatic efforts continue."

Beckett said Britain still had not been granted consular access to the captive sailors and marines, who have been held by Iran since March 23.

Earlier Tuesday, Prime Minister Tony Blair warned that Britain would "take an increasingly tougher position" if diplomatic moves did not yield results.

Beckett said Blair was not talking about military action.

"We are not seeking confrontation," she said. "We are seeking to resolve this through diplomatic channels."

Meanwhile, Iran's Fars News Agency issued a new picture of detained British personnel in an apparent breach of the understanding that no more such photographs would be published.

The picture, apparently a still taken from a video, showed six troops sitting in blue and red tracksuits on a carpet in a room. What appears to be a little bowl of nuts stood in the middle of the group.

The caption says: "British sailors are chatting and eating fruit, drinking coffee and playing chess. It seems that the sailors are satisfied with their situation, in which they are enjoying good conditions instead of working in a hard situation in the Persian Gulf."

Faye Turney, the only woman among the captured, was shown without a headscarf. She had worn one in initial images released of the Royal Navy crew.

The navy crew was detained March 23 by naval units of the Iranian Revolutionary Guards while the Britons patrolled for smugglers near the mouth of the Shatt al-Arab, a waterway that long has been a disputed dividing line between Iraq and Iran.

Iran says the team was in Iranian waters. Britain insists it was in Iraqi waters working under a U.N. mandate.

Iran has previously demanded an apology from Britain as a condition for the sailors' release.

On Monday, Iranian's top international negotiator Ali Larijani said that Iran sought "to solve the problem through proper diplomatic channels" and proposed having a delegation determine whether British forces had strayed into Iranian territory.

Larijani told Britain's Channel 4 news Monday through an interpreter that Iranian officials "definitely believe that this issue can be resolved and there is no need for any trial."

Iranian state-run media said all 15 of the detained Royal Navy personnel had confessed to illegally entering Iranian waters but the confessions would not be broadcast because of what it called "positive changes" in the negotiating stance of Britain.

The radio did not elaborate on the supposed changes by the British. But in London, a British official, speaking on condition of anonymity because of the sensitivity of the issue, said Blair's government had agreed to consider ways to avoid such situations in the future.

The official insisted Britain was not negotiating with the Iranians and still wanted the captives freed unconditionally.

Visit's Iran Center for complete coverage.