Italian Prime Minister Mario Monti convened a high-level security committee on Friday to reconstruct the events that led to the deaths of an Italian and a British hostage in Nigeria after the United Kingdom had ordered a rescue operation to save them.

The incident threatened to boil over into a diplomatic row, with officials in Rome calling for clarification about why London had not notified the Italian government that a rescue operation had been launched.

"It needs to be clarified why the British authorities decided to launch a military operation without informing us. We will get to the bottom of this," said former Italian Prime Minister Massimo D'Alema, the chairman of the parliamentary committee dealing with security issues.

British Prime Minister David Cameron said that British and Nigerian forces launched a joint operation to save the two hostages from their Islamist extremist captors when "a window of opportunity arose to secure their release."

"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 released," Cameron said.

A release from Monti's office said that although British and Italian authorities had kept "in close cooperation" since the hostages were kidnapped, Rome had "only been informed once the operation was already underway."

Captors' affiliation unclear

Italian national Franco Lamolinara and British national Chris McManus were kidnapped by gunmen in May 2011 in the city of Birnin, the capital of Nigeria's Kebbi state. The two engineers had been working on the construction of a bank there.

Nigerian President Goodluck Jonathan issued a statement on Thursday condemning the killing of the two hostages, saying those responsible had been arrested. Goodluck identified the captors for the first time as members of the Islamist extremist group Boko Haram, whose name means "Western education is sacrilege" in the local Hausa language. The group has been responsible for a series of deadly suicide bombings and shootings in Nigeria.

"The president, who particularly commended the cooperation and understanding of the British and Italian governments, assured that the perpetrators of the murderous act, who have all been arrested, would be made to face the full wrath of the law," the statement read.

In August 2011, a video emerged of the hostages, who said they were being held by al-Qaeda. This could not be independently verified at the time.

slk/acb (AP, AFP, dpa, Reuters)