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

The French advance towards the jihadist strongholds came amid reports that the Al-Qaeda linked militants were abandoning some of their positions and converging on the mountainous region of Kidal, their northernmost bastion, 1,500 kilometres (900 miles) from 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. We will not leave any pockets" of resistance, French Defence Minister Le Drian said on France 5 television.

Le Drian 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 a brazen hostage attack in neighbouring Algeria that rocked the world.

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

Fifty Senegalese soldiers arrived in the Mali capital Bamako, taking the number of African troops there to 150. The planned force will comprise 5,800 soldiers, but deployment has been slow, hampered by cash and logistical constraints.

And 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."

French troops on the ground meanwhile 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 northeast of the Malian capital and 60 kilometres 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 which could help serve as a base for operations further north. It is about 630 kilometres northeast of Bamako.

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 about nine months.

"We are in a phase of pushing forward," said a French lieutenant-colonel in charge of operations in Niono and the town of Diabaly, whose fate remains unclear.

Defence Minister Le Drian however said that "everything points to a favourable evolution of the situation in Diabaly in the coming hours."

The region where the towns are located is known for housing 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.

Asked 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."

"And the Russians have proposed to provide means of transport for the French, so it's fairly diverse," he said.

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

Germany Foreign Minister Guido Westerwelle responded to the appeal, saying "the African troops need financial aid" and pledging to do its bit without setting an amount.