Chris McManus was killed with Franco Lamolinara in Sokoto during an attempted rescue operation

UPDATE: According to Reuters, the Italian President has described British action in the Nigerian hostage operation as "inexplicable behaviour". Rome has demanded a political and diplomatic explanation.

An Italian politician has complained that David Cameron and the British Government took unilateral action in the failed attempt to free a British and Italian hostage in Nigeria.

Chris McManus and Franco Lamolinara were killed in Sokoto during an attempted rescue operation after being taken hostage in the country last May.

In a statement, Cameron said that he had authorised a rescue mission to go ahead today, saying there was "reason to believe that their lives were under imminent and growing danger."

"Preparations were made to mount an operation to attempt to rescue Chris and Franco. Together with the Nigerian Government, today I authorised it to go ahead, with UK support,” he said.

According to Downing Street, the British government was in contact with Italian authorities “throughout the case".

However, Lucio Malan, of the Italian People of Freedom party, questioned why the British government did not inform Italian counterparts of its intentions before launching the operation.

He told BBC2's Newsnight: "It is still to be explained why the Italian authorities were not informed although they are quite present on the territory of Nigeria."

Labour MP Meg Hillier, who chairs the all-party parliamentary group on Nigeria, said: "I don't know how fast moving this was but it does seem odd that an ally like Italy was not actually kept informed and it is important that we find out what happened and that the Prime Minister explains to the Italians."

Mr McManus, a contract worker for the construction company B.Stabilini, had been held by terrorists associated with Islamist extremist group Boko Haram since May last year after being kidnapped from his apartment by gunmen in Nigeria where he was helping to build a bank.

Mr Cameron said: "The terrorists holding the two hostages made very clear threats to take their lives, including in a video that was posted on the internet. Preparations were made to mount an operation to attempt to rescue Chris and Franco. Together with the Nigerian government, I authorised it to go ahead, with UK support."

Exact details of how Mr McManus died in Sokoto, a city in the north-west of Nigeria, remain unclear, but Mr Cameron said initial indications were that the contractor and Mr Lamolinara were "murdered by their captors, before they could be rescued". A Nigerian official claimed the two died in a crossfire during the rescue attempt, but the UK said it was awaiting further details.

Mr Cameron offered his "sincerest condolences" to the families of the hostages, saying they had "endured a terrible ordeal" after details of the failed mission emerged. In a statement, the family of Mr McManus, from Oldham, said they were "devastated by the news of Chris' death" but confident "everything that could be done was being done" during their 10-month ordeal.