The army of the Democratic Republic of Congo (DRC) has launched an assault against rebels in the volatile east of the country.

The offensive, which began on Tuesday in South Kivu province, is targeting a group called the Democratic Forces for the Liberation of Rwanda (FDLR).

Army sources told Al Jazeera that the rebels had fled into the forest when they were attacked. No civilians were caught in the fighting since they had evacuated the area, according to the sources.

FDLR fighters confirmed that they had been attacked but also said they had retaliated.

Why did the UN withdraw its support for the offensive?

The rebel group includes Rwandan Hutus who took part in the 1994 genocide and then fled across the border.

In the DRC, the fighters remain active in areas surrounding Lake Kivu, which has large natural gas reserves.

The FDLR is believed to number between 1,500 and 2,000 fighters. The rebels have been accused of numerous atrocities, including murder, rape, and recruitment of child soldiers.

The Congolese army faces similar accusations of human rights abuses.

Al Jazeera's Malcolm Webb, reporting from Kampala, the capital of neighbouring Uganda, said previous attempts to defeat the FDLR have placed civilians in the crossfire, and that the local population was gravely concerned that they would get caught up in the violence again.

The military assault could take months or even years, our correspondent said, adding that many had doubted the political will of the DRC and other countries involved to fight the FDLR.

The DRC "owes it to its people" to end the threat posed by Rwandan Hutu rebels, the outgoing US special envoy said on Tuesday.

Rebels 'comfortable' 

Russ Feingold said getting rid of the rebel threat was "an international responsibility".

"I was told back in May that the FDLR are 'comfortable' in eastern DRC. This is unacceptable," Feingold said in his last official speech before stepping down in coming weeks as US envoy to the Great Lakes and DRC.

"No armed group, especially one with a list of committed atrocities as long as that of the FDLR, should be comfortable."

Sharing what he called his "frustrations" that the FDLR had been allowed to shelter for so long in eastern DRC, Feingold urged that the group's wanted leader Sylvestre Mudacumura should be captured and stand trial.

The fresh assault against the group was first announced by President Joseph Kabila's government last month, with strategic, logistical, and operational support initially offered by the UN mission MONUSCO, which includes a brigade with a special UN mandate to take the offensive against armed groups.

However, MONUSCO withdrew the offer when Kinshasa refused to remove two generals designated to lead the campaign, Bruno Mandevu and Sikabwe Fall, with both men having been accused of abuses by the UN.

The Hutu rebels are accused of taking part in the 1994 mass slaughter of about 800,000 people in Rwanda, mainly from the Tutsi minority, before a Tutsi-led rebel front seized power.

The international community last year told FDLR to surrender by January 2, but barely 300 fighters turned themselves in. 

Source: Al Jazeera and agencies