The UN mission in the Democratic Republic of Congo (DRC), known as MONUSCO, is on high alert after fighting broke out between the M23 rebel group and the Congolese army on Thursday, UN spokesman Martin Nesirky said here Friday.

Congolese army on Thursday, UN spokesman Martin Nesirky said here Friday.

"Clashes erupted between the M23 and the FARDC, the Congolese army, in the Kibumba area, 25 kilometers north east of Goma in the Democratic Republic of the Congo," Nesirky said at a daily press briefing here, adding that MONUSCO has called it "the most serious incident since July."

The UN mission "is on high alert and has deployed quick reaction teams in Goma and at the airport, as well as in Kibati, on the main road between Kibumba and Goma," he said.

"The UN has reports that the Congolese army repulsed the attack and that the situation in Kibumba today is calm but very tense," Nesirky said. "Unconfirmed reports indicate that the M23 sustained a high number of casualties in the clash."

He also cited humanitarian partners as saying that 1,500 to 2, 500 people may have fled the region, due to the outbreak of violence.

In October, the UN Security Council expressed its intention to apply targeted sanctions against the leadership of the M23 armed rebel group in the DRC.

The M23 is composed of a breakaway faction of soldiers from the DRC's national army. It recently seized seven towns in North Kivu province and intensified attacks on schools, hospitals, homes and other civilian targets.