Algeria warned other nations to prepare for a higher body count after a four-day siege of a gas plant by Islamist militants ended in a bloodbath, amid fears as many as 50 hostages may have died.

Prime Minister Abdelmalek Sellal was expected to unveil the final grim tally at a 1330 GMT press conference on Monday.

French Defense Minister Jean-Yves Le Drian said Sunday the end goal of France's military action in Mali was to retake control of the whole country from Islamist militants who have seized the north.

"The goal is the total reconquest of Mali. We will not leave any pockets" of resistance, Le Drian said on France 5 television.

French forces are advancing towards Mali's Islamist-held north after taking up positions in the towns of Niono and Sevare, a spokesman for the French military operation codenamed Serval said Sunday.

"The deployment towards the north of the forces of Operation Serval, which began 24 hours ago, is on course with troops inside the towns of Niono and Sevare," Lieutenant Colonel Emmanuel Dosseur told reporters.

French Foreign Minister Laurent Fabius said Sunday that Russia had offered to help transport French troops and supplies to Mali and that Canada was to help to bring African troops to the country.

Asked on Europe 1 radio about how African troops would be transported, Fabius said "there is transportation that will be partly by the Africans themselves, partly by the Europeans and partly by the Canadians."

West African leaders Saturday sought urgent U.N. aid for a regional force to fight Islamists in Mali as President Francois Hollande said French troops would remain as long as needed to stamp out "terrorism".

The emergency summit of the Economic Community of West African States (ECOWAS) regional bloc also called on member states and Chad, which has pledged 2,000 troops, to put words into action without haste.

Residents of the Islamist-held northern Mali town of Gao on Saturday killed a local jihadist leader to avenge the murder of a journalist, an official said.

Sema Maiga, a deputy of the town's mayor, said the Islamists beat local journalist Kader Toure to death after accusing him of "working for the enemy", adding that residents then "killed an Islamist chief called Alioune Toure".

French President Francois Hollande Saturday came out in support of Algeria's deadly military strike against Islamist hostage-takers at a desert gas plant, saying the action was appropriate in the face of "coldly determined terrorists".

Other nations have criticized the hasty military backlash that left several expatriate workers dead, with Britain, Japan and Norway insisting they should have been forewarned of an army raid Thursday.

The U.S. State Department has ordered all family members of embassy employees to leave Mali, amid the country's escalating conflict with Islamist militants who control the vast arid north.

The order late Friday follows a tumultuous week in which gunmen across the border in Algeria staged a deadly raid on a remote gas plant, taking an unknown number of foreign hostages.

A dramatic four-day hostage crisis at an Algerian gas plant ended in a bloodbath Saturday when Islamists executed all seven of their remaining foreign captives as troops stormed the desert complex.

Twenty-one hostages, including an unknown number of foreigners, died during the siege that began when the al-Qaida-linked gunmen attacked the facility deep in the Sahara at dawn on Wednesday, the interior ministry said.

Two soldiers were killed and five others injured Saturday in an explosion in Okene city in Nigeria's central Kogi state, an army spokesman said, adding that they were part of the contingent set to be deployed to Mali.

"We lost two soldiers while five others were wounded when the IED (improvised explosive device) planted on their route went off and hit their convoy," Major General Bola Koleoso told Agence France Presse.