"Pending the outcome of an investigation, everything seems to indicate that the two French hostages were executed," said Thierry Burkhard, a spokesman for the armed forces in the defence ministry.

The two Frenchmen, both 25, were seized at gunpoint by suspected Al-Qaeda-linked militants from a restaurant in Niamey on Friday and died during a France-Niger rescue bid in the desert Saturday, officials said.

One of them was a former aid worker who had been due to marry a local woman next week. According to the Journal du Dimanche the other was his best man, who had just arrived in Niamey to act as witness at the ceremony when the two were snatched late Friday.

Burkhard said a French surveillance aircraft backed up Niger armed forces that chased the kidnappers and caught up with them in the desert, enabling troops on the ground to attack.

A commander in the Niger forces was wounded in a first clash with the kidnappers, he said.

The aircraft then pursued the captors further and a second fight took place in which "several" of the kidnappers were killed and two French ground troops slightly injured, Burkhard said.

A statement from French Defence Minister Alain Juppe on Saturday said: "At the end of the operation, the lifeless bodies of the two hostages were discovered."

The hostage's local member of parliament named them as Antoine de Leocour, who had worked in Niger, and Vincent Delory, who had grown up together on the same street in the small northern French town of Linselles.

"Vincent's father... didn't want his son to go there. His son had no reason to go, except for his friend's marriage," said the MP Christian Vanneste.

French President Nicolas Sarkozy on Saturday condemned the killings as "a barbarous and cowardly act."

A military source in Mali said the kidnapping may have been carried out on behalf of Al-Qaeda in the Islamic Maghreb (AQMI), which has claimed other abductions in the Sahel desert region spanning Niger, Mali, Mauritania and Algeria.

The group in July killed a 78-year-old French hostage three months after he was kidnapped in Niger, in revenge for the killing of six AQMI members in a failed Mauritanian-French rescue raid.

In September, gunmen raided the Niger mining town of Arlit and abducted five French nationals, along with a Togolese and a Madagascan. They are now believed to be held in Mali by AQIM.

The French foreign ministry warned French nationals against travel to the Sahel region.

"In light of the terrorist threat in the region, no place can be considered safe," the foreign ministry said on its website, urging them to exercise "the greatest vigilance."