The FDLR has long been established in eastern DR Congo
Civilians in eastern Democratic Republic of Congo have subjected to escalating reprisals at the hands of armed groups, aid agencies say.
The atrocities, which include rape and arson, come amid continuing fighting between the army and Hutu militiamen.
In the Lubero territory in North Kivu 250 homes were been burned down in the last week, Oxfam said.
In Luofo, a nearby village, Hutu rebels are said to be conducting a house-to-house terror campaign.
Local authorities say rebels operating in the village, which is 170km (274 miles) from the regional capital, Goma, have been telling those they visit "you will all die", according to the UN refugee agency, UNHCR.
'Not enough peacekeepers'
Fighters from the FDLR rebel group torched more than 365 homes in Luofo and Kasiki on 17-18 April, UNHCR said.
In the town of Lubero and the surrounding area, the situation is "rapidly worsening", the agency said.
Several thousand homes have been set on fire since military operations began in January, according to Oxfam.
An Oxfam official who recently visited Lubero said one woman had spoken of a neighbour being gang-raped by three armed men.
There were too few UN peacekeeping troops patrolling the affected area, leaving people scared and vulnerable, the agency said.
The UN said the FDLR had stepped up raids since Congolese and Rwandan troops ended a joint offensive against the rebel group in mid-February.
It also said that tensions were rising between locals in Rutshuru, 80km north of Goma, and people displaced during intense fighting in the region last autumn.
Many of the FDLR fled to DR Congo after the 1994 Rwandan genocide, in which some its leaders were accused of taking part.
The group's presence in the east of the vast country has been seen as a major factor in the region's instability since then.