A rescue mission which ended in the deaths of a British and Italian hostage was the "best chance" to rescue the two men alive, Defence Secretary Philip Hammond has said.
Chris McManus, 28, from Greater Manchester, and Franco Lamolinara died in the attempt by UK Special Forces and Nigerian military on 8 March.
The two men were working as engineers when they were captured by Islamist militants nine months ago.
In a statement to the Commons on 13 March 2012, the defence secretary gave more details about the rescue mission.
Mr Hammond said information had been received that necessitated an immediate rescue effort, and that the Italian government was informed of the operation "as soon as possible afterwards".
"The military judgment was the hostages were facing an imminent and escalating threat and while an immediate rescue attempt would inevitably involve risk it represented the best chance of securing the release of Chris and Franco alive."
Mr Hammond said the bodies of the two hostages were found by the rescue team on entering the compound.
They had been murdered by their captors with automatic gunfire, he added.
He said their deaths were a "terrible tragedy", and told MPs a coroner's inquest into the death of Mr McManus would be held.
Labour supported the government's decision to launch the rescue mission.
Shadow defence secretary Jim Murphy said the two hostages had been killed in "cold blood" and that those responsible for their deaths "must be pursued".
He asked for further details of relations between the UK and Italian governments, after the Italian President criticised the UK over the handling of the operation.
Giorgio Napolitano said it was "inexplicable" that the UK did not give his government advance notice of the rescue attempt.
Mr Hammond told the Commons that discussions between the two governments over the weekend had "substantially diffused" the situation.
Labour MP Michael Meacher, Mr McManus's constituency MP, paid tribute to Mr McManus's family for their "unceasing" efforts to secure his release throughout his captivity.