GENEVA — United Nations investigators said on Tuesday that hundreds of men, women and children were slaughtered and thousands driven from their homes in attacks by one ethnic group on another in the Democratic Republic of Congo last year, and that the assaults may have amounted to crimes against humanity.

The attacks took place in December near Yumbi, a town in western Congo, Ravina Shamdasani, a spokeswoman for the United Nations human rights office in Geneva, told reporters on Tuesday, citing the investigators’ report.

Ms. Shamdasani said that villagers of the Batende ethnic group, armed with hunting rifles, machetes, bows and arrows and gasoline, killed at least 535 villagers during attacks on a Banunu community. The death toll was likely to have been much higher, she added, echoing earlier United Nations reports that close to 900 people had died.

In January, United Nations investigators traveled to the region on a two-day mission and interviewed 90 people. They determined that around 19,000 people had fled the violence, about 16,000 of whom crossed the border into the neighboring Republic of Congo, Ms. Shamdasani said. The attackers also destroyed close to a thousand buildings, mostly houses but also including 14 churches, 17 schools and several health centers.