Hostages in Nigeria killed before rescue attempt The men were abducted in northwestern Nigeria last May Nigeria and Britain launched a rescue effort to free the hostages The men were believed to be in "imminent" danger, British PM says (CNN) -- A Briton and Italian held hostage for 10 months in northern Nigeria died Thursday, apparently killed by their captors before they could be rescued, the British prime minister said. Nigerian security forces, with support from Britain, launched an operation Thursday to free British citizen Chris McManus and Italian national Franco Lamolinara, Prime Minister David Cameron said. But the effort did not succeed. "It is with great regret that I have to say that both Chris and Franco have lost their lives," Cameron said in a statement. We are still awaiting confirmation of the details, but the early indications are clear that both men were murdered by their captors, before they could be rescued. Cameron said British and Nigerian authorities have been working hard to free the hostages since they were kidnapped May 12. "The terrorists holding the two hostages made very clear threats to take their lives, including in a video that was posted on the Internet," Cameron said. The prime minister said authorities couldn't locate the men for months, but eventually "received credible information about their location" and "a window of opportunity arose to secure their release." We also had 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," Cameron said. Italian Prime Minister Mario Monti said said an "unpredicted acceleration of events took place over the last hours. While fearing an imminent danger for the hostages, Nigerian authorities activated the rescue. He said Italian authorities were alerted once the operation began. Both leaders expressed their condolences to the families of the victims. Cameron thanked Nigerian authorities, Nigerian President Goodluck Jonathan and British authorities for their efforts. The McManus family said in a statement that Chris "was in an extremely dangerous situation. However we knew that everything that could be done was being done. The family said they are "devastated" by the development and grieving over their loss. Our thoughts are also of course with the loved ones of Chris' colleague, Franco Lamolinara, who are also coming to terms with this truly sad news. A video showing two Westerners abducted in Nigeria last spring surfaced in August. The men worked as engineers for an Italian construction company based in Nigeria, according to Agence France Presse. Gunmen stormed their apartment in Birnin Kebbi, the capital of Kebbi state in northwestern Nigeria, and kidnapped them, AFP said. However, Kebbi is on the border with Niger, where al Qaeda in the Islamic Maghreb has claimed abductions of foreign workers. AFP received a video at its office in the Ivory Coast city of Abidjan last summer in which a speaker said that the two men had been abducted by al Qaeda. The hostages were "blindfolded and on their knees, with three men holding weapons standing behind them, their faces hidden by turbans," AFP said. The agency reported that video "was accompanied by photographs which showed the men without blindfolds." It said that the hostages identified themselves and delivered statements "urging their governments to meet the demands of the kidnappers, whom they say are from al Qaeda in the Islamic Maghreb."