Italian authorities are expressing anger that Thursday's attempted rescue of a British and an Italian hostage in Nigeria was apparently authorized without their input.

The head of a parliamentary committee on Italian national security, Massimo d'Alema, says Britain needs to clarify why it did not discuss the operation with Italy before beginning.

Italian security officials and lawmakers are to meet to go over the details of the failed rescue. The two hostages, Italian national Franco Lamolinara and British national Christopher McManus, were killed by their captors before they could be rescued.

British Prime Minister David Cameron said Thursday he approved the joint British and Nigerian operation after getting information of the men's location and that their lives were in “imminent and growing danger.”

Mr. Cameron apparently informed Italian Prime Minister Mario Monti in a phone call after the operation was underway.

Nigerian President Goodluck Jonathan blamed the Boko Haram militant group for the kidnappings and said that all the kidnappers have been arrested, without specifying how many. British and Nigerian officials say they believe the captors were from an al-Qaida-linked splinter cell of Boko Haram, rather than from the group's main leadership.

The hostages were kidnapped in May in northern Nigeria. They later appeared in an Internet video with armed gunmen who claimed to be with the al-Qaida terrorist network.

Kidnappings are not uncommon in Nigeria's delta region, where tensions over oil profits run high, but they are rare in northwestern Nigeria where Sokoto is located, near the border with Niger.