Claims that Iran masterminded the kidnap of five British contractors in Baghdad were played down by UK and Iraqi officials tonight.
The release of computer expert Peter Moore after more than two and a half years in captivity sparked fresh questions about who was behind the highly-organised abduction in 2007.
General David Petraeus, the former US commander in Iraq, told the BBC he was "90% certain" the hostages were held in Iran for at least part of their ordeal.
The Guardian reported that the kidnapping was led by Iran's Revolutionary Guard, with the Britons taken to prison camps inside Iran within a day of their capture.
But the Foreign Office insisted it had seen nothing to back up the claim.
A spokesman said: "We have seen speculation that Iran is directly involved in this kidnapping. Iran of course has an influence in Iraq, but we have no evidence to substantiate claims of direct involvement in the kidnapping.
"We have no evidence that the British hostages, including Peter Moore, were held in Iran. We are not in a position to say with any certainty where they were held during each and every single day of their two and a half years in captivity."
Mr Moore, 36, from Lincoln, was seized along with his four British bodyguards by militants posing as police at the finance ministry in Baghdad on May 29 2007.
After lengthy negotiations for his release, he was freed yesterday and is expected to return to the UK within days.
A photograph taken of him at the British Embassy in Baghdad today shows him looking healthy but gaunter than in previous pictures and with grey flecks in his hair.
The bodies of three of the security guards - Alec MacLachlan, 30, from Llanelli, South Wales, Jason Swindlehurst, 38, from Skelmersdale, Lancashire, and Jason Creswell, 39, originally from Glasgow - were passed to UK authorities earlier this year.
Prime Minister Gordon Brown and Foreign Secretary David Miliband have demanded the return of the remains of the final hostage, Alan McMenemy, 34, from Glasgow, who they believe has also been killed.
Mr Brown today spoke by phone to his Iraqi counterpart Nouri al-Maliki to thank him for his efforts in Mr Moore's release and express his gratitude to all those who secured his safe return.
Today's media reports will further heighten tension between the UK and Iran after Britain renewed its calls for human rights to be respected over the clampdown on protesters in Tehran and other cities.
Amid rising diplomatic tensions, Iran's foreign minister Manouchehr Mottaki said this week that Britain would "receive a punch on the mouth" if it did not "stop its nonsense".
Iranian state television today dismissed claims that Tehran was behind the kidnapping as "part of a psychological war against Iran".
An Iraqi MP involved in negotiating for the British hostages' release denied that Iran had any involvement in the kidnapping.
The Guardian reported that Sami al-Askari, an adviser to Mr al-Maliki, flew to Qom in Iran several times to meet the leader of the kidnappers.
But Mr al-Askari told the BBC he had not visited Iran for negotiations, although he said he had been involved in talks with the hostage-takers in Iraq.
A senior member of the Shi'ite group widely blamed for the abductions, Asaib al-Haq or the League of Righteousness, also denied Mr Moore had been taken to Iran.
Sheikh Jassim al-Saidi said: "He was not held in Iran, and you can ask the hostage. He knew where he was. He hadn't been in Iran a single day."
He added that Mr al-Maliki had promised the group that its leader Qais al-Khazali would be freed soon.
Khazali, who was suspected of involvement in a 2007 attack in Karbala which led to the death of five American soldiers, was passed over from US custody into the hands of the Iraqi authorities at around the same time as Mr Moore's release, prompting speculation of a prisoner exchange deal.
But the Foreign Office insisted the cases were "completely separate" and Mr Miliband said no "substantive concessions" were made to the hostage-takers by the UK.
Canon Andrew White, the Anglican chaplain to Iraq who has been dubbed the Vicar of Baghdad, said today that he maintained talks to secure Mr Moore's release until three days before Christmas.
He held many face-to-face meetings with intermediaries that often took place late at night and lasted many hours.
Canon White said he was assured that the release would happen after the Muslim holy day of Ashura on December 27 - but only learned that it was definitely happening early yesterday morning.Reuse content