PARIS (AP) -- France is "at war" with al Qaeda and will step up efforts to fight the terrorist group's North African offshoot after it executed a French hostage in the Sahara, Prime Minister Francois Fillon said Tuesday.
Mr. Fillon acknowledged that the group may have killed 78-year-old hostage Michel Germaneau before -- not after -- a failed last-ditch raid to try to free him.
Al Qaeda in the Islamic Maghreb said in an audio message broadcast Sunday that it had killed Mr. Germaneau in retaliation for a raid last week by Mauritanian and French forces that killed at least six al Qaeda militants.
French President Nicolas Sarkozy confirmed the killing Monday, vowing that the perpetrators "will not go unpunished."
His prime minister said Tuesday that France will reinforce efforts to work with governments in northwest Africa fighting al Qaeda in the sparsely populated swath of desert that includes the borders dividing Mauritania, Mali, Algeria and Niger.
"We are at war against al Qaeda," Mr. Fillon said on Europe-1 radio. He said, without elaborating, that France "thwarts several attacks every year."
French Foreign Minister Bernard Kouchner said Tuesday from Mauritania that the Sahel region in question "will not be left to terrorist bands, arms and drug traffickers."
"The combat risks being long, but we will continue it," Mr. Kouchner said after meeting with Mauritanian President Mohamed Ould Abdel Aziz. Mr. Sarkozy sent the minister to the region this week to discuss, among other things, security for French citizens.
Mr. Fillon said it was unclear when Mr. Germaneau was killed. He said French authorities considered the possibility that the hostage "had already been dead" at the time of a July 12 ultimatum issued by the terrorist group. Mr. Fillon said that was only an "assumption" based on "the abnormal, strange character of this ultimatum and of (the group's) refusal to engage in discussion with French authorities."
French forces agreed to take part in what he called a "last-chance" operation in the hope they could still save Mr. Germaneau, the prime minister said.
Asked whether France would seek to find Mr. Germaneau's remains, Mr. Fillon said only that when British hostage Edwin Dyer was beheaded in the region last year, "his remains were never found."
Al Qaeda in the Islamic Maghreb, or North Africa, grew out of an Islamist insurgency movement in Algeria, formally merging with al Qaeda in 2006 and spreading through the Sahel region.
Amid increasing concerns about terrorism and trafficking in northwest Africa, Algeria, Mauritania, Mali and Niger opened a joint military headquarters deep in the desert in April to respond jointly to threats from traffickers and the al Qaeda offshoot.
Associated Press writer Ahmed Mohammed contributed to this report from Nouakchott, Mauritania.