KINSHASA - Around 12,000 people have fled recent fighting between rival factions of the M23 rebel group in eastern Democratic Republic of Congo, the UN refugee agency said Tuesday, as a local doctor warned of "methodic" rape in the troubled country.

"We estimate that around 4,000 households, or around 12,000 people, have been displaced in the zone of Rutshuru" in North-Kivu province, Simplice Kpanji of the UN High Commissioner for Refugees (UNHCR) in Kinshasa told AFP.

Some people have fled to Ishasha, a government-controlled post on the border with Uganda, he said, while around 1,000 "have settled in Kiwandja, near to the base of the UN mission MONUSCO".

Some 1,500 more were sheltering in a primary school at a military base in the northeastern town of Rumangabo which serves as the headquarters of M23.

A doctor in South Kivu province meanwhile raised the alarm on the "methodic, systematic and massive" rape of women in the strife-ridden region.

According to Denis Mukwege, whose local charity Panzi helps rape victims, the rate of sexual assault went up in 2012 and looks set to be as high in 2013, he warned.

Mukwege told a press conference in Kinshasa on Tuesday that he receives around 300 victims of rape or sexual assault for treatment every month.

For the past two decades, DR Congo's mineral rich east has been a haven for armed groups who have left a trail of bloodshed and killing in their wake, and raped tens of thousands of women.

Violence surged again last May when the Congolese army began fighting the M23 rebel group, formed by army mutineers.

But despite a peace deal signed on February 24 by 11 African nations to bring stability to the region, infighting continues between two factions of the M23.

One faction supports the movement's military chief, General Sultani Makenga, while the other is loyal to its political leader Jean-Marie Runiga.

The M23 was founded by former fighters in a Tutsi rebel group whose members were integrated into the regular army under a 2009 peace deal that they claim was never fully implemented. DR Congo's neighbours Rwanda and Uganda are suspected of financing the rebels but deny the accusations.

According to UNHCR, 500,000 people have been displaced in North Kivu, the heart of the M23 rebellion, since the resurge in fighting last May, while a total 2.6 million have fled their homes across eastern DR Congo.