BAMAKO: The African Union urged NATO powers Tuesday to send forces to help a regional West African force retake northern Mali from Islamist guerillas, as rebel fighters closed in on Malian forces.

"NATO should play a part and the African force would lead the way as was done by NATO in Afghanistan," said the African Union's chairman, Benin's President Thomas Boni Yayi, at a news conference in Canada.

The West African desert nation of Mali has been cut in two since early last year, when Tuareg rebels -- including Islamist fighters -- seized control of cities in the arid north and east of the country.

Mali's regional allies have vowed to help the government recapture the territory, which some fear could turn into a rear base for terror gangs, and the United Nations has endorsed plans for an international force.

Addressing a joint news conference with Canadian Prime Minister Stephen Harper during a visit to Ottawa, Yayi said: "I think that NATO should add its forces to our efforts so this could be an international mission.

"This is an international situation," he added.

Several NATO members -- including the United States, Canada and France -- have offered to help train and supply the West African force bolstering Mali's army, but none have offered Western boots on the ground.

"The Canadian government is not considering a direct military mission," Harper told reporters, echoing previous comments in Washington and Paris.

But he added: "Obviously we are very concerned about the situation, and the development of essentially an entire terrorist region is of grave concern to everybody in the international community."

Overnight Malian soldiers had fired warning shots at Islamist fighters amid fears they plan to advance on the government-controlled south of the country, a military source said.

The fighters retreated after the shots were fired at Kona near the town of Mopti, which lies about 650 kilometres (400 miles) northeast of the capital Bamako, the source told AFP.

Mopti is the first major town south of a vast swathe of desert which fell into the hands of armed Islamist groups and Tuareg rebels after a coup that rocked Bamako last March.

The incident was the first time Malian soldiers and rebel forces have come into direct confrontation since the Islamist movements sidelined their Tuareg separatist allies last year.

Security sources and witnesses have said that three Islamist rebel groups had set up a military base in Bambara Maoude, a town near Timbuktu.

These movements -- the Al-Qaeda-linked Ansar Dine, the Movement for Oneness and Jihad in West Africa and Al-Qaeda in the Islamic Maghreb -- control Timbuktu, Kidal and Gao, the regional administrative centres in northern Mali.

Security sources claim they have been joined by members of Boko Haram, an extremist movement blamed for thousands of deaths in nearby Nigeria.

One regional security source said he was "deeply worried" and suspected the Islamists planned to head southwards into government-held territory.

Ansar Dine and another armed group in the north, the ethnic Tuareg Azawad National Liberation Movement (MNLA), are homegrown movements, while the other two movements have infiltrated the vast territory.

The Islamists have effectively sidelined the MNLA, and peace talks planned between Ansar Dine, its former Tuareg ally and the government that were due to begin on Thursday in Burkina Faso were postponed indefinitely on Tuesday.

The Economic Community of West African States theoretically has 3,300 troops on standby for a mission to reclaim northern Mali that received the approval of the UN Security Council on December 20.

But the United Nations has also called for negotiations between armed groups and the Bamako government, and Western military sources cast doubt on the ability of a regional force to fight guerillas in unfamiliar desert terrain.

Moreover, in November, UN special representative for the Sahel Romano Prodi said that no intervention could take place before September 2013, to allow time for the preparation of the African force.