Algerian helicopters on Thursday launched strikes on a gas complex where Al Qaeda-linked Islamists are holding 41 foreign hostages, injuring several of them, a spokesman for the kidnappers told a Mauritanian news agency.

"Two Japanese were injured," the unnamed Islamist source from "The Signatories of Blood" group of former AQIM leader Mokhtar Belmokhtar which claimed the attack, told the ANI news agency.

The militants said they seized the hostages, who are known to include US, French, British, Irish, Norwegian and Japanese citizens, in retaliation for the French military intervention in northern Mali.

Algerian media reported Thursday that 15 foreigners and 30 Algerians being held hostage had managed to escape, but authorities could not confirm this.

Algerian troops encircled the plant on Thursday, prompting gunmen to demand their withdrawal to allow for negotiations.

They have also demanded the release of some 100 Islamist extremists in Algeria, and want them sent to northern Mali, where French and Malian troops were battling extremists who seized a massive swathe of territory in April 2012.