NAIROBI — More than 1,400 civilians were deliberately killed this year in eastern Congo during two successive military operations, and the United Nations urgently needs “a new approach to protect civilians,” according to a Human Rights Watch report to be released Monday.

The report, based on months of research and more than 600 interviews, paints a bleak and brutal picture of eastern Congo, which has been ravaged by civil war for more than a decade. The presence of about 19,000 United Nations peacekeepers has not seemed able to stop the slaughter.

Among the atrocities listed by Human Rights Watch researchers were cases of girls being summarily killed after being raped, and other victims being tied together before their throats were slit.

The 183-page report also said: “Government representatives said the operations would bring peace and security to the region. They have not.” It called the attacks against civilians “vicious and widespread.”

The Human Rights Watch report is likely to add to the growing criticism of the United Nations peacekeeping mission in Congo, which many advocacy groups say has failed and must be reformed to protect civilians adequately.

Next week, the United Nations Security Council is expected to vote on whether to extend the peacekeepers’ mandate, and one proposal calls for much tighter conditions on any cooperation between the peacekeepers and the Congolese military.

In the past month or so, several other reports have examined the increasingly violent atmosphere in eastern Congo, where the bloodshed has been fueled by ethnic tensions, competing commercial interests, land disputes and regional politics playing out at gunpoint. The area is rich in resources like gold, diamonds, copper, tin and the metallic ore coltan, but still desperately poor because most minerals are stolen by renegade soldiers.

Last month, a group of experts working for the Security Council issued a report that laid out, in unprecedented detail, how the rebels finance their brutality, tracing the flow of illegal minerals from Congo to Uganda, Burundi and Rwanda, and eventually to markets in Europe or smelters in Asia. The report asserted that government officials in several African countries were working with the rebels to smuggle out minerals and bring in guns.

Earlier this year, the Congolese Army went on the offensive against some of those rebel groups, and the United Nations provided logistical support. But the offensive failed to wipe out the rebels, and human rights groups have said that the military operations spurred the massacre of civilians, including by the government troops who were getting United Nations help.

The United Nations peacekeeping department had been warned by its legal advisers about the risks of working so closely with a notoriously ill-disciplined army, according to documents provided to The New York Times last week. The operation went ahead anyway.