French Prime Minister Francois Fillon has said the two Frenchmen killed in Niger were shot dead in cold blood by their captors during a failed rescue.
He also said he was “almost certain” the pair, Antoine de Leocour and Vincent Delory, were the victims of al-Qaeda in the Islamic Maghreb (Aqim).
The men’s bodies were found after the operation on the Niger-Mali border.
France has defended the action, arguing that doing nothing would have signalled that France does not fight terrorism.
Defence Minister Alain Juppe has flown to Niger to speak to the authorities about the situation and to meet some of the French community.
“It was a serious, difficult decision but we took it and we take full responsibility,” he said on Sunday night, adding that President Nicolas Sarkozy had made the decision to intervene.
French forces and helicopters were also involved in the mission.
The two men, both 25, were abducted by four gunmen from a restaurant in the capital Niamey on Friday night.
Mr Fillon has suggested they were murdered as the attempted rescue took place the following day.
“The hostage-takers, seeing they were pursued, killed the hostages in cold blood, according to the first elements in my possession,” he said.
But a senior Niger military official told Reuters news agency that the bodies were found away from the scene of the clash, implying that they were probably “executed” before the rescue mission.
Relatives have reportedly asked to see the bodies.
French anti-terror police have already arrived in Niger to investigate the deaths.
State of shock
Mr de Leocour had worked for a non-governmental organisation in Niger for several years.
He was due to get married to a local woman next week and Mr Delory, who was to be his best man, had flown in for the wedding.
The two friends had grown up together on the same street in the small northern French town of Linselles.
“I’m in no state to talk right now, I’m in shock, I can’t believe it,” said Mr Leocour’s fiancee, Rakia Hassan Kouka.
“I’m going to pray for them, so that they can go to paradise,” she told AFP.
Another childhood friend of Mr Leocour who travelled to Niger for the wedding spoke to France’s Europe 1 radio station.
“We came to see him married and now we’re going to see him buried,” said the man named only as Louis. “I am torn between pain and hatred.”
It is reported to be the first time French nationals have been abducted in the capital city Niamey.
Six others have been kidnapped in Niger since last April but mostly from more remote desert areas.