Sudan ? A large force of Sudanese soldiers backed by allied janjaweed militiamen is sweeping through North Darfur, killing civilians and looting and burning villages in violation of a cease-fire agreement, international observers and rebels said Sunday.

At least four civilians were killed near the northern town of Birmaza on Sunday, said Youssouf Mussabal, a rebel leader in the area. Some 200 pro-government janjaweed fighters riding camels had moved into the zone, backed by mobile army units and the Sudanese air force, he added.

Another rebel field commander from a separate faction said seven villages were looted and burned to the ground around Birmaza on Sunday. Jar al-Naby said the renewed government offensive began last week, and that two civilians were killed in Friday raids.

Hundreds of cattle have also been rounded and brought back to the Sudanese army headquarters in the North Darfur town of Mellit, al-Naby said by telephone from Darfur.