Two western hostages held in Nigeria have been killed during a joint Nigerian-British rescue mission after 10 months in captivity, British Prime Minister David Cameron said on Thursday. He said it appeared Briton Chris McManus and Italian Franco Lamolinara had been "murdered by their captors before they could be rescued." Both had been working for an Italian construction firm in Nigeria, and had been taken hostage by terrorists in northern Nigeria in May, said Cameron. "After months of not knowing where they were being held, we received credible information about their location," dpa quoted Cameron as saying in a televised statement from Downing Street. "A window of opportunity arose to secure their release," he said, adding that there was reason to believe that the men's lives were "under imminent and growing danger." "Together with the Nigerian government, today I authorized it to go ahead, with UK support," said Cameron. He had learned of the tragic outcome from Nigerian President Goodluck Jonathan, said Cameron, and had subsequently informed his Italian counterpart, Mario Monti, of the news. "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," said Cameron. The two engineers were kidnapped near Kebbi, in north-west Nigeria, on May 12, 2011. "I am very sorry that this ended so tragically," said Cameron.