Nigeria has sent an air force technical team and the commander of a planned African-led force to Mali to assist the country's military as it battles Islamists, a presidency spokesman said Saturday.

The confirmation of Nigerian military personnel on the ground comes after French air power helped Mali mount an offensive against the Islamists who control the country's north and who have been seeking to push further south.

However, it was not yet clear when a planned 3,000-strong African-led force could be sent despite 15-nation west African bloc ECOWAS giving its go-ahead on Friday for the immediate deployment of troops.

The Islamists' advance in Mali has raised fears that the country could provide a safe haven for Al Qaeda-linked extremists, posing a threat to the region as well as Europe and beyond.

Nigeria has the largest military in the 15-nation Economic Community of West African States, but it is also battling an insurgency by Islamist extremist group Boko Haram at home in its northern and central regions.

"The technical staff from the Nigerian air force are already on the ground in Mali," Nigerian presidency spokesman Reuben Abati told AFP. "They are not fighters; they are technical staff."

He added the commander of the planned African-led force, a Nigerian, was also in Mali.

A Nigerian defence spokesman had earlier said the country had not sent any troops to Mali. Abati maintained the statement was "factually correct to the extent that the Nigerian troops are not yet on the ground. The foot soldiers are not yet there."

The Nigerian air force team was there to "assess infrastructure, to provide back-end support and to help maintain the Malian air force," Abati said.

He did not have further details on their activities, including when they were deployed, how many air force staff were there and how long they would remain.

Nigerian troops would later be deployed as part of the planned African-led force that has been approved by the UN Security Council, he said. Abati could not provide numbers, but Nigeria has previously spoken of sending 600 troops.

The UN Security Council has approved the 3,000-strong force, but it is not expected to be ready to deploy before September.

Mali's army said Nigerian and Senegalese forces were involved in Friday's offensive against the Islamists which was backed by French air power. Dakar has denied having any troops there.

Friday's offensive saw Mali and French air power unleash a counter-attack against Islamist fighters, recapturing the central town of Kona after it had been lost to the rebels as they advanced south from their northern strongholds.

French President Francois Hollande confirmed that French forces were supporting the Malian offensive aimed at repelling the Al-Qaeda-linked radicals.

While he gave no indication of the scale of French involvement he said it would last for as long as necessary.

US officials meanwhile suggested they might support the French action there with surveillance drones and aerial refuelling tankers.

Mali's army is considered too weak to tackle the Islamist groups who seized the north last year, taking advantage of the power vacuum created by a coup in Bamako.