KINSHASA - Ugandan LRA rebels have kidnapped at least 700 people in attacks in Democratic Republic of Congo and the Central African Republic since February last year, a human rights group says.

Human Rights Watch said in a report that the Lord's Resistance Army "has abducted more than 697 adults and children in a largely unreported campaign in the Central African Republic and the neighbouring Bas-Uele district of northern DRC".

"Nearly one-third of those abducted have been children, many of whom are being forced to serve as soldiers or are being used for sex by the group's fighters."

HRW carried out an investigation in the two countries between July 12 and August 11, interviewing 520 civilians "including 90 former kidnap victims".

The human rights group said: "The LRA brutally killed adults and children who tried to escape, walked too slowly, or were unable to bear the heavy loads they were made to carry."

Senior Africa researcher at HRW Anneke van Woudenberg said: "The LRA continues its horrific campaign to replenish its ranks by brutally tearing children from their villages and forcing them to fight. The evidence points to Joseph Kony, the LRA leader, as the author of this atrocious campaign."

The LRA, led by war crimes suspect Kony, who is wanted by the International Criminal Court in The Hague, first took up arms against the government in northern Uganda in 1988, waging a brutal rebel war that displaced scores of thousands.

But since 2005, under pressure from the Ugandan army, the LRA has moved into remote outlying areas in neighbouring countries, including the DRC, the Central African Republic and the south of Sudan.

The New York-based non-governmental organisation said the Ugandan rebels "often attack villages early in the morning or late in the day, when residents are likely to be home. LRA fighters grab their victims and tie them to each other by the waist, forming long human chains.

"The abductions are usually followed by the extensive looting of food, clothes, salt and other items, which are loaded into heavy bundles onto the captives' heads, backs and shoulders before they are marched off into the forest," it said.

During one of their latest incursions at the end of May in north-eastern DRC, LRA fighters "attacked many villages near Ango, the territorial capital (of the Bas-Uele district), abducting 23 people, including 16 children", it added.

"Human Rights Watch found that abducted children are separated from the adults and kept close to the LRA commanders. They are rarely released.

"They quickly learn to obey the LRA's rules and to speak Acholi, the commanders' language, and are exposed to immense brutality to integrate them into the group. The LRA forces many children, as part of their indoctrination, to kill other children who try to escape or fail to obey the rules."

Traumatised child witnesses who spoke to HRW described being forced to kill dozens of adults who reached an LRA camp in the DRC to prevent them from giving its location to government soldiers or the Ugandan army.

The report said the military presence to fight the LRA in the DRC was short of what was needed in terms of transport and communications equipment.

The HRW urged the US "to swiftly carry out the legislation signed by President Barack Obama on May 26 to develop a comprehensive strategy to protect civilians in Africa from LRA attacks" and bring LRA leaders to justice.