LONDON (AFP) -International pressure mounted on Iran on Sunday to free 15 British naval personnel but British authorities admitted they do not know where the group are being held.

The British ambassador in Tehran again demanded the release of the eight Royal Navy sailors and seven Royal Marines but got no response, officials said.

The 14 men and one woman were seized on the Shatt al-Arab waterway that divides Iraq and Iran on Friday. Britain says they were conducting “routine” anti-smuggling operations. Iran said Saturday that the group has admitted illegally entering Iranian waters.

“We don’t know where they are. We wish we did. We are asking whether they are being moved around inside Iran,” Lord David Triesman, a Foreign Office junior minister, said in an interview with Sky News television.

The British ambassador to Tehran, Geoffrey Adams, met senior officials at the Iranian foreign ministry on Sunday to seek the freedom of the group, a Foreign Office spokesman in London told AFP.

Adams “pressed again for the release of our personnel, asked where they are being held and for consular access”, he added.

Iran’s foreign ministry provided no immediate response and further meetings were a possibility, he added.

Triesman again denied that the group from HMS Cornwall had deliberately entered Iranian territory.

“We’ve been very clear throughout that the British sailors don’t intentionally enter into Iranian waters,” he said. “There’s no reason for them to do so. We don’t intend to do so. and I think people should accept that there’s good faith in that assertion.”

On Saturday, the Germany presidency of the European Union called for their “immediate release” and said Germany’s ambassador to Tehran had also spoken with the Iranian government about the matter.

Iran’s ambassador to London has twice been summoned to the Foreign Office. On Friday he met a senior civil servant and Triesman on Saturday.

Triesman said Britain wanted the Iranians to reassure the group’s families that they were in good health and unharmed.

The group’s seizure comes three years after eight British Royal Navy personnel training their Iraqi counterparts on the same stretch of waterway were detained for three days by Iran.

They were blindfolded, paraded on Iranian television and apologised for their actions — although Britain denied illegal encroachment — before being released.

Triesman said that while negotiations were “very difficult and delicate”, he was confident that there would be a “good outcome” to the latest incident.

But it comes amid a much different political situation, with Britain and Western governments at loggerheads with Iran over its disputed nuclear programme.

The United Nations Security Council on Saturday unanimously voted to impose new sanctions on Iran over its refusal to abandon uranium enrichment.

Newspapers have expressed fears the sailors might be used as a bargaining chip in the mounting war of words over the nuclear crisis. One speculated that the sailors detention looked like a “hostage crisis”.

“The source of a dispute matters less than the leverage Tehran thinks it can extract from it,” The Guardian said.

Iran has accused the British military of seeking to “create a climate of tension at a moment when a resolution on Iran is to be put to the vote, despite the fact that Iran seeks calm and stability in the region”.

“The questioning of the British sailors is continuing to try to establish their real intentions,” he added.

Triesman was asked Sunday about any possible links between the two events but played down the suggestion.

“We have been assured that’s not the case. Our own view is that these things aren’t linked,” he said.