At least 40 people have been killed and scores more wounded in fierce overnight fighting between Yemeni forces and supporters of an anti-U.S. rebel cleric, security sources say.
They said clashes between the army and followers of Hussein al-Houthi erupted again on Wednesday after a weeks-long lull, when efforts to mediate an end to the fighting failed.
The clashes, in the northern mountainous province of Saada, began after the government launched an offensive against Houthi and his supporters on June 20.
The sources did not give a breakdown for Wednesday's casualties. Officials say at least 179 people have so far been killed since June 20, but Houthi's supporters put the death toll at more than 200.
The government accuses Houthi, leader of the "Believing Youth" group and a Zaidi Shi'ite sect, of setting up unlicensed religious centres and of forming an armed group which has staged violent protests against the United States and Israel.
It has offered a $54,000 (29,600 pounds) reward for his capture.
Government sources said hundreds of Houthi supporters have been wounded, arrested or surrendered to authorities in Saada, 240 km (150 miles), north of the capital Sanaa.
Anti-U.S. sentiment is high in Yemen and other countries in the Middle East over the presence of U.S. troops in Iraq and the Israeli-Palestinian conflict.
Yemen, a poor country of some 19 million people, is also fighting to root out militants linked to Saudi-born Osama bin Laden's al Qaeda network. Houthi has not been accused of links to the group.