Nine Congolese soldiers were ambushed and killed by Rwandan Hutu rebels in the eastern Democratic Republic of Congo, a military source said Tuesday, over a month after the army launched a sweeping offensive against the militias.

The attack by the Democratic Forces for the Liberation of Rwanda (FDLR) happened Monday afternoon in eastern Masisi district of North Kivu, DR Congo, Major General Leo
Mushale, who commands forces in the northeast of the country, said.

Three officers were among the dead, including commander of Masisi district Colonel Raphael Bawili, He said at a press conference in Goma, the capital of North Kivu.

"The enemy was able to carry out this ambush because a number of Congolese continue to collaborate with them," said the general.

"We have not yet eradicated the FDLR but they are being neutralised by our forces and we ask the public not to collaborate with the enemy," he added.

In late February DR Congo forces launched a fresh offensive against rebels active in the restive eastern provinces of North and South Kivu.

The FDLR, a militia of Rwandan Hutu rebels, has been active in DR Congo since crossing over the border from Rwanda after the 1994 genocide of Tutsi people and the subsequent seizure of power by a Tutsi-led rebel faction.

Some of the Hutu militia's older commanders and soldiers are wanted by international courts for their alleged role in the massacre, which claimed the lives of some 800,000 people in Rwanda, mainly from the Tutsi minority.

Since the launch of the operation five weeks ago, the army claimed to have "neutralised" a few hundred rebels, according to General Mushale, out of a fighting force of around 2,000.

Mushale confirmed only that 13 rebels had been killed and refused to give the total number of army losses.

In late March, the UN security council voted to cut 2,000 troops from the 20,000-strong peacekeeping force in the country, despite calls by Kinshasa for UN troops to hand over responsibility for security to the country's army.