The Italian government was warned by David Cameron that a team was on its way to Nigeria to free two kidnapped engineers nine months before the disastrous rescue bid went ahead, political insiders have claimed.
His comments came as a furious row erupted over claims by the Italian government that it was not told about plans to rescue Briton Chris McManus and Italian Franco Lamolinara who were being held hostage.
Both men were killed by their captors during the rescue mission.
Political commentator Paul Waugh said by tweet that the Italian government had been aware of the plans for nine months.
The rescue bid was discussed by the Cabinet's emergency Cobra committee for those nine months, he said.
"I'm not aware of any objections [to the planned raid]," said Waugh.
British diplomatic sources dismissed Italian claims that they were told about the military operation only after it had started. They said any protests by Rome were disingenuous.
Cameron said he gave the go-ahead to the operation because the men's lives were in "imminent and growing danger".
"A window of opportunity arose to secure their release," he explained. Monti's press officer said he had asked Nigerian president Goodluck Jonathan to provide a detailed reconstruction of events.
Corriere della Sera newspaper said Italian public opinion had been "humiliated" by Britain.
"British responsibilities over the military operation are clear: Italy was not informed that a military operation was taking place in Nigeria," reads an editorial.
"The United Kingdom is still acting under nostalgia for its imperial glory that leads it to take unilateral action when it comes to military intervention."
Some reports said the kidnappers turned their guns on the hostages before the joint British and Nigerian military operation entered the compound where they were kept.
Jonathan blamed Islamist terrorist sect Boko Haram for the killing.
The Independent newspaper claimed that the group were planning to sell the hostages to a more extreme faction who may have murdered them.
The kidnappers call themselves "al-Qaeda in the Land Beyond the Shael" and are thought to be part of the Boko Haram group that has carried out bombing and arson attacks across northern Nigeria.
The British rescue team was in Nigeria for more than two weeks to plan for the raid on the compound.
"[The kidnappers] wanted the Nigerian government to release prisoners but they couldn't say which prisoners they were talking about," a source told The Daily Telegraph. "We had intercepted phone calls that the hostages were to be transferred and killed."