In a statement late Tuesday, Prime Minister Tony Blair's office said there had been "further contacts" between the two countries, including with chief international negotiator Ali Larijani.
"The UK has proposed direct bilateral discussions and awaits an Iranian response on when these can begin," Blair's office said. "Both sides share a desire for an early resolution to this issue through direct talks."
British officials say there has been intense diplomatic activity, including meetings in London with Iran's ambassador. But reports of contacts with officials in Tehran have been sketchy. The Downing Street statement did not say whether the contact with Larijani came in person or by phone.
Blair said earlier in the day that the next 48 hours would be "fairly critical" to resolving the standoff over the British personnel, who have been held by Iran since March 23.
The call for talks came hours after Iranian diplomat Jalal Sharafi was freed by his captors in Iraq.
He had been seized Feb. 4 by uniformed gunmen in Karradah, a Shiite-controlled district of Baghdad.
His release raised hope for an end to the standoff and suggested the possibility of a de facto prisoner swap - something both Tehran and London have publicly discounted.
Iran alleged the diplomat had been abducted by an Iraqi military unit commanded by U.S. forces - a charge repeated by several Iraqi Shiite lawmakers. U.S. authorities denied any role in his disappearance.
In Baghdad, an Iraqi Foreign Ministry official said the Iraqi government had exerted pressure on those holding Sharafi to release him - but he would not identify who had held Sharafi.
But another senior government official said Iraqi intelligence had been holding him. Both officials spoke on condition of anonymity because they were not supposed to release the information. Sharafi was a second secretary at the Iranian Embassy involved in plans to open a branch of the Iranian national bank. U.S. officials allege that Iran provides money and weapons to Iraqi Shiite militias. Sharafi was abducted a month after the U.S. military arrested five other Iranians in northern Iraq. The U.S. described one of those captives as a senior officer of the Quds Force, an elite unit of Iran's Revolutionary Guards. The Iraqi Foreign Ministry official said his government also was working "intensively" for the release of the five other Iranians to "help in the release of the British sailors and marines." Neither Iran nor Iraq nor Britain has said explicitly that a prisoner swap was in the works. Iran has denied it seized the Britons to force the release of Iranians held in Iraq, and Britain has steadfastly insisted it would not negotiate for the sailors' freedom. In Washington, President Bush signaled the same. "I also strongly support the prime minister's declaration that there should be no quid pro quos when it comes to the hostages," Bush said. It was unclear whether the Iraqis had won Sharafi's freedom on their own initiative to encourage a settlement, which would ease tension without endangering their own claim to the waters where it occurred. Nevertheless, the release of Sharafi and efforts to free the five other Iranians suggested that the parameters of a deal might be taking shape. Iran maintains the British sailors had encroached on Iranian territory when they were seized by naval units of the Revolutionary Guards on March 23. Britain insists its sailors and marines were in Iraqi waters and has demanded their unconditional release. Iran's official Islamic Republic News Agency quoted First Vice President Parviz Davoodi as saying that "Britain should accept that it has invaded Iranian waters and guarantee that it will not be repeated." "The violation was clear and obvious and all evidences and documents were suggesting occurrence of the violation," Davoodi added. "Britain has recently changed its approach and shifted toward legal and diplomatic negotiations." With the standoff at a sensitive stage, Britain reacted with caution to the release Tuesday of new pictures of the British captives on the Web site of Iran's Fars News Agency. The images showed six sailors sitting on a carpet in a room, wearing blue, black and red tracksuits. Two sailors were shown playing chess. Faye Turney, the only woman among the captured, was shown without a head scarf. She had worn one in initial images released of the Royal Navy crew. Britain has expressed outrage over the airing of earlier videos in which Turney and others "confessed" to violating Iranian territorial waters. The latest pictures did not show any further confessions. And as tensions have escalated, the Iranians have appeared to back off somewhat. Larijani's suggestion Monday of talks over territorial disputes in the Persian Gulf had offered the hope of an end to the crisis, the British premier acknowledged. But if negotiations to win the quick release of the 15 sailors and marines stalled, Britain would "take an increasingly tougher position," Blair said. Larijani said Monday 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 in the Gulf. He did not say what sort of delegation he had in mind. Larijani told Britain's Channel 4 news Monday through an interpreter that Iranian officials believed there was no need for any trial of the navy crew. (AP) Associated Press Writer Nasser Karimi in Tehran, Iran, and Robert H. Reid in Amman, Jordan, contributed to this report. AP-CS-04-03-07 1959EDT