Yemeni forces have killed at least 12 militants in southern Abyan province, just days after the government said it had “liberated” the provincial capital of Zinjibar from Islamist fighters.

Army officials said Wednesday negotiations with southern militants to end the bloodshed there are deadlocked. The Yemeni government has been fighting to retake control of Zinjibar and other parts of Abyan from al-Qaida-linked fighters who seized the area in May.

Later, at least two explosions hit the intelligence headquarters and a police base in the southern coastal city of Aden, causing little damage.

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.

On Tuesday, the U.N. High Commissioner for Human Rights said 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.