Ethnic Tuareg rebels have launched a fierce offensive against Mali's security forces in a bid to seize the northern town of Kidal. 

The attack on Saturday is further evidence that Tuareg rebels have significantly increased their attacks against government control in Mali.

Kidal is the latest and most significant town targeted by the fighters, who have gained ground in other northern areas following weeks of clashes with government forces.

The Tuareg rebels have been bolstered by an influx of fighters from Libya who joined their movement after the late Libyan leader Muammar Gaddafi was toppled last year.

Hama Sidahmed, a Europe-based spokesman for the rebels, said their ambition was to take control over Kidal.

"We will take the two military camps and occupy the town."

The sporadic firing of heavy weapons have been heard across the town as government forces fought to fend off the fighters, according the Reuters news agency. 

In recent days, thousands of civilians reportedly fled the town in anticipation of the fighting.

Civilians fleeing

Some Tuareg leaders say many of their community have also fled the southern city of Bamako, fearing reprisals after violent demonstrations this week.

About 3,500 people had crossed west into Mauritania, said a Mauritanian official, speaking on the condition of anonymity.

The International Committee for the Red Cross (ICRC) said on Friday that nearly 10,000 people had fled into Niger after fighting between the army and armed groups in the area around the northeastern cities of Menaka and Anderamboucane.

Other aid officials say more than 5,000 others have fled to Mauritania.

The Tuareg rebels say they are fighting to secure the independence of Azawad, an area that takes in Mali's three northern regions, one of which is Kidal.

The government accused the rebels of atrocities and collaborating with al-Qaeda, a charge rejected by the MNLA.

The ICRC said that some refugees were being looked after by local families while others had set up makeshift camps nearby.