An upsurge in violence involving government troops and militia in eastern Democratic Republic of Congo has forced 100,000 people from their homes since November, the UN refugee agency said Friday.

The cause of the spike has not yet been established, the UN High Commissioner for Refugees said, but it follows fraud-tainted elections that month.

Attacks between rival militia groups in North Kivu's Walikale and Masisi territories are thought to have left 22 dead and an unidentified number of women were raped, with 35,000 fleeing their homes to escape the violence, according to the agency.

Humanitarian officials who visited the affected areas last week found empty and burned villages, UNHCR spokesman Adrian Edwards told journalists in Geneva.

Clashes in Shabunda in South Kivu have meanwhile forced an estimated 70,000 from their homes since November.

The UNHCR said government troops, Rwandan rebel group FDLR and local defence groups were behind the violence.

"We are trying to get a sense of what the reason is for this upsurge," Edwards said. "We are obviously in the aftermath of elections -- it may be related to that."

DR Congo President Joseph Kabila fought off rigging accusations to secure a second term following the November 28 poll.

The full results of legislative elections held the same day will be released later this month, the country's electoral commission said.