KHARTOUM (Reuters) - Sudanese government forces and a rebel faction have clashed in north Darfur, two rebel groups said on Friday.

Mohamed Abdullah, a commander with a faction of the Sudan Liberation Army (SLA) headed by Abdel-Wahed Mohamed el-Nur, said his group lost two fighters but captured a number of government vehicles and weapons in the clash on Thursday.

A spokesman for the Sudanese military could not confirm the incident but said the army had troops operating in north Darfur.

Noureddine Mezni, a spokesman for the joint United Nations/African Union peacekeeping force (UNAMID), said: "We have initial information about clashes in the area. We are monitoring the situation." He did not give further details.

The clashes came a week after Sudanese President Omar Hassan al-Bashir launched a national initiative to end the five-year-old conflict. Rebel groups boycotted the event.

Suleiman Jamous, a leader of another SLA/Unity group in north Darfur, said both forces clashed when they confronted each other "by accident" on a road near the area of Anabaji.

Abdullah and Jamous said government forces overtook a rebel base in the Helf area in north Darfur on Thursday night.

"There will be retaliation," Abdullah told Reuters.

International experts estimate that 200,000 have died and 2.5 million fled their homes since mostly African rebels took up arms against the Arab-dominated government in 2003, charging it with neglect. The government says 10,000 have lost their lives and accuses the international media of exaggerating the crisis.