Algerian troops ended a siege by Islamist militants at a gas plant in the Sahara desert where 23 hostages died, with a final assault which killed all the remaining hostage-takers, Reuters said.

Believed to be among the 32 dead militants was their leader, Abdul Rahman al-Nigeri, a Nigerien close to al Qaeda-linked commander Mokhtar Belmokhtar, presumed mastermind of the raid.

An Algerian interior ministry statement on the death toll gave no breakdown of the number of foreigners among hostages killed since the plant was seized before dawn on Wednesday, January 16.

Details are only slowly emerging on what happened during the siege, which marked a serious escalation of unrest in northwestern Africa, where French forces are ratcheting up a war against Islamist militants in neighboring Mali.

Algeria's interior ministry said on Saturday that 107 foreign hostages and 685 Algerian hostages had survived, but did not give a detailed breakdown of those who died.

The Islamists' attack has tested Algeria's relations with the outside world, exposed the vulnerability of multinational oil operations in the Sahara and pushed Islamist radicalism in northern Africa to center stage.

Some Western governments expressed frustration at not being informed of the Algerian authorities' plans to storm the complex. Algeria, scarred by a civil war with Islamist insurgents in the 1990s which claimed 200,000 lives, had insisted there would be no negotiation in the face of terrorism.