But diplomats said negotiations which came to a close late on Wednesday night would resume on Thursday. The discussions pertain to the conditions of the release.
One British diplomat said he had visited the six Royal Marines and two naval personnel.
"They were fit, well and well-treated," he said, adding he took messages from them to their families.
Iranian Foreign Minister Kamal Kharazi at a news conference earlier on Wednesday had announced men would be freed.
"Since it was clear that they had no aim of entering Iranian border waters, and basically they had entered Iranian territorial waters by mistake, they will be released today [Wednesday]," Kharazi is quoted as saying.
"The British warships which had entered Iranian border waters were confiscated and the soldiers were captured and were investigated."
Kharazi acknowledged that the
sailors entered Iran by mistake
Iranian television had broadcast footage of two of the arrested sailors apologising for entering Iranian territorial waters.
"The team wrongly entered Iranian waters and we apologise for this mistake because it was a big mistake," one of the sailors, identified as Sergeant Thomas Hawkins, said in comments dubbed into Arabic and shown on Iran's Al-Alam television on Tuesday.
It was also reported that the sailors would leave Iran without the three military patrol boats and unspecified equipment.
Hawkins, dressed in military fatigues, said his team had been one mile inside Iranian territorial waters when they were arrested by Iran's Revolutionary Guards.
The sailors will leave Iran without
their boats and equipment
Another sailor, chief petty officer Robert Webster, said the group had wrongly entered Iranian waters on a mission accompanying a vessel from Umm Qasr to Basra.
Earlier, British diplomats landed in Khuzestan in southwest Iran for the handover of the servicemen held since Monday.
The arrests threatened to cause a serious diplomatic rift between Iran and Britain.
"We have just landed in Ahvaz," one diplomat said, speaking from the provincial capital of Khuzestan, the oil-rich province on the Iraqi border. They arrived from the Iranian capital Tehran.