U.N. peacekeepers in Congo are violating the laws of war and should immediately stop backing Congolese troops who have deliberately killed hundreds of civilians in an operation to oust rebels in eastern Congo, Human Rights Watch said.

Human Rights Watch said it had documented "vicious and widespread" attacks against civilians by soldiers and rebels between January and September. Soldiers being fed and supplied with ammunition by the United Nations have killed civilians, gang-raped girls and cut the heads off some young men, human rights and international aid groups said.

"For every rebel combatant disarmed, one civilian has been killed, seven women and girls have been raped, six houses have been burned and destroyed and 900 people have been forced to flee their homes," the British-based organization Oxfam said.

Human Rights Watch said it documented the killings of 732 civilians between January and September by the Congolese army and troops from neighboring Rwanda fighting alongside it. In the same period, it counted 701 civilians killed by the Rwandan Hutu rebels the U.N.-backed troops are fighting.

"Some chopped to death by machete, some hacked to death, others burned in their homes, some clubbed to death by sticks or bats," Anneke Van Woudenberg, the senior researcher for Human Rights Watch in Congo, told a news conference in New York City on Monday. "These were not civilians who got caught in the crossfire; these were not civilians who were in the wrong place in the wrong time. These were civilians who were deliberately targeted."

Most of the victims were women, children and the elderly, she said.

More than 7,500 cases of sexual violence against women and girls were registered at health centers during that nine-month period, nearly double the amount in 2008 and likely representing only a fraction of the total.

Human Rights Watch said the 19,000 peacekeepers in Congo _ the biggest U.N. force in the world _ must "immediately cease all support to the current military operation."

The peacekeepers should also arrest 15 known human rights abusers in the army that the U.N. itself has identified, includingBosco Ntaganda, who is wanted by the International Criminal Court for war crimes, she said. Ntaganda is a former Congolese rebel commander whose forces were integrated into the national army.

To continue support for the Congolese military operations while knowing that abuses are being committed implicates both the United Nations and its peacekeeping mission in the human rights violations, Van Woudenberg charged.