Britain said on Saturday (March 31) it was concerned at Iranian "sabre-rattling" about possibly putting captured British naval personnel on trial and for the first time voiced regret the incident had occurred. Iran's ambassador to Moscow said the 15 Britons captured eight days ago could face punishment if found guilty of illegally entering the Islamic Republic's territorial waters. British Foreign Secretary Maragaret Beckett said Britain had sent Iran a written reply to its diplomatic note on the detention of the sailors and had so far received no response. "One never publishes the contents of such notes and so I can't say to you either, much about the proposals, all I would say to you is that what we are endeavouring to do, is as we have done from the beginning to encourage Iran to move to a way to peacefully resolve this issue," Beckett told reporters after a European Union foreign ministers' meeting in Germany. "We continue to seek knowledge of where our people are held, access to them and a speedy and safe resolution of the issue. Those are the key things and we are looking all the time for ways to pursue that," she added. Iran seized the sailors and marines in the northern Gulf on March 23 when they were on a U.N.-backed mission searching for smugglers. Tehran says they strayed into Iranian waters but Britain insists they were well in Iraqi territory. The crisis, at a time of heightened Middle East tensions over Iran's nuclear ambitions, has helped push oil prices to six-month highs over concerns an escalation might cut oil exports from the region. Iran's Foreign Ministry delivered a letter to Britain's embassy in Tehran on Thursday, the first written communication between the two capitals since the crisis began. The IRNA news agency said the Iranian message asked for "necessary guarantees that violations against Iranian waters would not be repeated". Beckett said: "As you may know it's very much a holiday period in Iran and ministries are not working at full stretch, people are away and so on." The Iranian government is largely shut down for the two-week Nowruz holiday, a pre-Islamic Persian new year, which began on March 21 and ends next Tuesday. But as Beckett says Britain would like to resolve the issue as soon as possible. "All I'm saying is, we continue to express our willingness to engage in dialogue and discussion to come to resolution of this issue, that is very much in the best interest of our people and our foremost concern," she said. EU foreign policy chief Javier Solana was mandated on Friday by the 27-nation bloc's foreign ministers to seek the Britons' immediate release. He said he had not yet been able to speak to Iranian leaders but his staff had made first contacts. Student members of the Basij religious militia from across Iran issued a statement on Saturday demanding the British embassy in Tehran be closed down, calling it the "corruption nest of the British old devil", IRNA said. They also invited students to protest outside the embassy on Sunday "to protest the violation of Iranian waters by British soldiers and the Security Council's latest statement," the student news agency ISNA said. Iran displayed three of the detained Britons on television on Friday and released a letter from one saying she was being held because of "oppressive" British and U.S. behaviour in Iraq. British forces have been deployed in southern Iraq since joining the U.S.-led invasion of the country in 2003. Britain and the United States accuse Iran of allowing sophisticated weapons used to target their forces to be brought into Iraq.