A British building contractor and his Italian colleague taken hostage in Nigeria were killed before rescuers could reach them.
Chris McManus, from the North-West, and Franco Lamolinara were taken hostage in Northern Nigeria in May 2011.
After their capture, the radical islamist group Boko Haram threatened the men's lives in a distressing video that was posted on the internet.
David Cameron said in a statement that after months of not knowing where the hostages were being held, officials received credible information about their location.
"A window of opportunity arose to secure their release," he said.
But the men are understood to have been murdered by their captors before special forces from Britain and Nigeria could reach them. The men's families have been informed of their deaths.
ITV's Rohit Kachroo asked the Foreign Secretary about rescue operations of this type during a visit to Somalia last month.
William Hague told him: “I don’t rule that out at all but I also don’t want to hold out the prospect that that is always going to be the answer."