According to an Iranian military source, the commander of the Revolutionary Guards has called for them to be freed.
Major-General Yahya Rahim Safavi is said to have told the country's Supreme National Security Council on Friday that the situation was "getting out of control" and urged its members to consider the immediate release of the prisoners to defuse tension in the Gulf.
However, Safavi's intervention was reportedly denounced by another senior general at a meeting of high-ranking commanders yesterday.
Yadollah Javani, the head of the Revolutionary Guards' political bureau, was said to have accused him of weakness and "liberal tendencies". Javani is said to have demanded that the prisoners be put on trial.
The developments followed a warning by Safavi, the Revolutionary Guards commander, that Iran should prepare for a possible invasion, which he believes could come as early as next month.
US military exercises in the Persian Gulf involving two aircraft carriers, 100 aircraft and 10,000 personnel have fuelled fears in Tehran that America may be on the verge of launching airstrikes against Iran's nuclear programme.
Many military officers believe the British naval party intercepted on March 23 was part of a ploy to test Iran's readiness for an invasion. Tens of thousands of Basij, the force that provided the shock troops for the Iran-Iraq war, have been sent to the Iraqi border.
Iranian military sources said the Supreme National Security Council had concluded on Friday evening that Ayatollah Khamenei, the supreme leader, should order the release of the British naval personnel on Safavi's advice.
Iran's ambassador to Moscow, Gholamreza Ansari, said a legal process was already underway. "If there is no guilt, they will be freed," he added. But he denied that he had said they could face trial. Other officials called on Britain to send a delegation to Tehran to resolve the crisis.