African nations rushed on Sunday to deploy a 3,300-strong force aimed at helping Mali retake its Islamist-controlled north, but questions remained over how they aimed to succeed in the daunting task.

Despite the risks, some African analysts and officials said Sunday there was no other choice but to act since the Al Qaeda-linked extremists and criminal gangs in Mali threatened to spread violence in the region and beyond.

The scramble to send troops came as French forces carried out air strikes in Mali for a third straight day and extended their bombing campaign to the northern strongholds of the Islamist forces.

A push by Islamists further south led to the French assault and resulted in an expedited plan for the African force, which has been approved by the UN Security Council but was not expected to deploy before September.

A clutch of regional nations have pledged nearly 3,000 troops so far for the mission with an expected total of four battalions.

The commander is Nigerian Major General Shehu Usman Abdulkadir, previously his country's chief of army standards and evaluation.

Senior officers from neighbouring countries were expected in Bamako on Sunday to prepare for the arrival of the first troops from the force, whose main organiser is the 15-nation Economic Community of West African States.

"The end goal is to take back the north and then flush out those elements," ECOWAS spokesman Sunny Ugoh said of "terrorists" and criminal gangs in Mali.

But taking back Mali's north, a territory the size of France, from Islamists said to be well-equipped could prove to be daunting.

Some analysts said logistical support, such as France's air power, would continue to be needed and possibly other assistance.

Discussions on the force have also included the possibility of 5,000 Malian troops, but doubts persist over the capabilities of Mali's military.

Algeria's stance has also been a source of speculation, and Malian Prime Minister Diango Cissoko arrived in Algiers on Sunday. The country shares a long border with Mali and its military has experience dealing with Islamist threats.

But while it has pledged support for Mali's regime and signalled it does not oppose foreign intervention, there was no sign Algeria would participate more directly.

Jibrin Ibrahim, head of the Nigeria-based Centre for Democracy and Development, urged quick action from the region, warning the risks of a continued Islamist advance could be catastrophic.

Asked whether 3,300 troops were enough, he said it was less about the number than the strategy employed and continued assistance from Western nations.

"The (Malian) troops on the ground were not very effective, but the fact that France provided aerial cover was what changed the situation on the ground," he said.

"I think the troops on the ground are very important, but that this will only work if it is a genuine international force."

Difficulties have already been encountered by French forces despite success in pushing the Islamists back.

French Defence Minister Jean-Yves Le Drian acknowledged that the unexpected advances made by the Islamists last week had not yet been fully reversed as officials admitted they were proving a tougher adversary than anticipated.

Aides to French President Francois Hollande described the militants as better equipped, armed and trained than expected.

A French military source said they preferred to act alone for the time being rather than mix with the African force as they would lose precious time otherwise, with the eventual goal of combining.

"In any case, this is the time it will take for (the African force) to arrive," the source said. "Afterward we can work in cooperation ..."

Among other countries, Britain has offered support in the form of transport planes and the United States is considering offering surveillance drones.

Germany has defended France's action but ruled out sending troops and warned that Mali's problems could only be solved by political mediation.

West Africa has had previous experience in deploying a multi-national force, particularly with the ECOMOG contingent first deployed in Liberia in 1990. It was both commended for helping bring peace and criticised for rights abuses.

Former Nigerian foreign minister Bolaji Akinyemi said the Mali operation risked raising tensions in the home countries of some participants, particularly Nigeria, which is battling its own insurgency by Islamist extremist group Boko Haram.

Nevertheless, the region must act to put an end to the threat, he said.

"If west African countries don't do anything about it, they will encourage this and it will grow further," he said.

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