French troops on Sunday consolidated gains in Mali's Islamist-held north as Paris said the aim was its "total reconquest" and Canada, Germany and Russia offered vital aid for the offensive.

The Al-Qaeda-linked group that shocked the world with its audacious hostage attack in neighbouring Algeria threatened meanwhile to stage further reprisal strikes on nations involved in chasing out Islamists from Mali.

The French advance towards the jihadist strongholds in Mali came amid reports that the militants were abandoning some of their positions and converging on the mountainous region of Kidal, their northernmost bastion, 1,500 kilometres (900 miles) from the capital Bamako and near the border with Algeria.

Kidal was the first town seized by an amalgam of Islamist militants and Tuareg separatist groups in March last year. The two sides then had a falling out and the Islamists have since gained the upper hand in the vast desert north.

"The goal is the total reconquest of Mali," French Defence Minister Le Drian said in televised remarks. "We will not leave any pockets" of resistance.

Le Drian also said seven French citizens taken hostage by Islamist militants in Niger and Mali in recent years were alive, adding there had been "contacts with the hostage-takers".

There had been fears over their fate since the start of the French military intervention in Mali, which sparked the brazen attack on a gas plant in neighbouring Algeria and hostage-taking that rocked the world.

The 72-hour stand-off ended in scores of deaths Saturday.

On Sunday, the assailants, calling themselves Signatories in Blood, vowed "more operations in all the countries which have taken part in the crusade against Azawad if they do not review their decision", using the Islamist name for northern Mali.

"We remind our Muslim brothers of the need to clear out from sites run by foreign companies, especially the French ones, to save their lives," their statement said.

Meanwhile 50 Senegalese soldiers arrived in the Mali capital Bamako, taking the number of African troops there to 150. And Benin said it was boosting its troop allotment for Mali to 650 soldiers from 300 planned earlier.

Senegal, Benin and six other west African nations -- Nigeria, Togo, Niger, Guinea, Ghana and Burkina Faso -- as well as Chad have announced their contributions to the mission that is to take over from France.

But deployment has been slow, hampered by cash and logistical constraints.

The head of the Commission of regional west African bloc ECOWAS, Desire Kadre Ouedraogo, estimated the cost of an African offensive against the armed Islamist groups at about 500 million dollars (about 375 million euros).

"But the figure may vary depending on needs," he told Ivory Coast's state television RTI.

So far estimates ranged between 150 and 200 million euros, with the European Union pledging 50 million euros.

"The international community must mobilise," he urged.

Meanwhile a radical Islamist group Ansaru on Sunday claimed responsibility for an attack in central Nigeria that killed two soldiers who were due to be deployed to Mali, injuring five others.

The regional powerhouse last week boosted its troop commitment for Mali to 1,200 soldiers from 900 planned earlier.

In a statement in poor English, Ansaru said: "We have successfully execute our first attempt in (crippling) the Nigerian army troops (whose aim was) to demolish the Islamic empire of Mali."

On the ground in Mali, French troops said they were buttressing their positions.

"The deployment towards the north... which began 24 hours ago, is on course with troops inside the towns of Niono and Sevare," Lieutenant Colonel Emmanuel Dosseur told reporters, referring to key frontline outposts.

Niono is about 350 kilometres (215 miles) northeast of the Malian capital and 60 kilometres (20 miles) south of Diabaly, which was seized nearly a week ago by Islamists and then heavily bombed by French planes.

Sevare has a strategically important airport about 630 kilometres (390 miles) northeast of Bamako that could help serve as a base for operations further north.

The town is also near Konna, whose seizure by Islamists on January 10 sparked the French military intervention in the former colony against the forces occupying northern Mali for the last nine months.

The region is home to what are considered the most martial and fanatical Islamists.

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

The announcement came a day after an emergency west African summit of the ECOWAS bloc called on the United Nations "to immediately provide financial and logistical backing for the deployment of MISMA", the African force.

German Foreign Minister Guido Westerwelle responded by acknowledging the need for financial aid and pledging to do its bit, without setting an amount.