A Yemeni military official and witnesses say government forces have killed at least 11 militants in the latest fighting in the southern province of Abyan.

They say the militants were killed in exchanges of fire with Yemeni troops Tuesday and Wednesday in and around the provincial capital, Zinjibar. The Yemeni government has been fighting to retake control of Zinjibar and other parts of Abyan from al-Qaida-linked militants who seized the areas in May.

Elsewhere, witnesses say Yemeni security forces have attacked anti-government tribesmen in the Arhab region north of the capital, Sana'a, killing at least nine people since Monday.

Opposition protesters and tribesmen have been protesting since February for an immediate end to Yemeni President Ali Abdullah Saleh's 33-year autocratic rule. Yemeni troops and Saleh loyalists have cracked down on demonstrators and tribesmen who have taken up arms against the government.

The U.N. High Commissioner for Human Rights said Tuesday hundreds of people have been killed in six-months of protest-related violence. The commissioner's office also accused the Yemeni government of using excessive lethal force against peaceful activists protesting for greater freedoms.