Bamako - Malian helicopter gunships bombed rebel positions near the key northern town of Kidal on Friday, a military official said, hours after former colonial power France called for a ceasefire and immediate talks to end a three-week rebel offensive.

France, which remains an ally of its former colonies, backed Bamako's stance against the rebels' claim for an independent north. In a further sign of disruption caused by clashes, the United States delayed its annual counter-terrorism training for its allies in the Sahara region.

Dozens of people have been reported killed on both sides and tens of thousands of civilians have been forced from their homes since the MNLA rebels, boosted by weapons and men from Libya, started attacking towns and military outposts in mid-January.

Last weekend, rebels had come within eight kilometres (5 miles) of Kidal, the capital of one of three northern regions they are targeting. But a Malian military official said they have since been pushed back by helicopter gunships, as well as heavy weapons fire by the armed forces.

"Five of our helicopters have been bombing the rebels ... to take out the attackers," the official said, adding that raids had taken place about 15 km from the town.

A second military source said: "We are not waiting for them to attack us anymore. Now it is us going on the offensive."

A rebel spokesman said he was not aware of any assaults on Friday. He said Malian military helicopters had tried to attack them on Wednesday and Thursday but there were no injuries.

Mali's military has the advantage of air power over the rebels but the MNLA pose the most robust threat yet to Bamako, even if they are not seen having the might to carve out an independent state in the north.