An Islamist militant killed by special forces during the siege of Algeria's In Amenas gas complex used to be a driver at the desert facility, a security source told AFP on Wednesday.

"One of the killed assailants had worked as a driver for one of the companies operating within the complex," the source said, adding that "he had resigned a year ago."

The source was unable to specify who the slain militant had worked for, but indicated that his corpse was recognised by employees at the remote facility deep in the Sahara where a four-day siege last week ended in a bloodbath.

Special forces launched two assaults aimed at freeing both foreigners and Algerians taken hostage inside the complex -- one on Thursday a day after the deadly drama unfolded and then in a final raid on Saturday.

On Monday, Prime Minister Abdelmalek Sellal said that 37 foreign hostages and 29 militants were killed.

Five foreigners are still missing and seven burned bodies remain unidentified.

Sellal said that most of the dead hostages were killed execution-style with a single bullet to the head.