Government forces are closing in on an
opposition cleric and his supporters in a mountainous region of northern Yemen, military sources say.
More than 150 troops and insurgents have been killed, including a rebel commander, in skirmishes.
The government accuses Sheikh Hussein al-Houthi, a leader of the Shia Zeidi sect, of forming an underground armed group and fomenting sectarian strife.
Battles were still raging in the Maran area, reports said.
Zeidis are a moderate Shia group living mainly in north-west Yemen.
President Ali Abdullah Saleh has called on Mr Houthi to turn himself in, promising him a fair trial.
"I call on you to surrender and I guarantee a fair process in the accusations against you," the president said in quotes carried by local media.
He said Mr Houthi's group had attacked mosques and urged Yemenis to arm themselves against possible attacks by the US.
The cleric had also said in his lectures that democracy would bring a Jewish leader to power in Yemen.
Dozens of Mr Houthi's supporters were reported to have turned themselves in early after violent fighting at dawn on Sunday.
Correspondents say the cleric, who served as an MP in Yemen's parliament from 1993 to 1997, enjoys the support of up to 3,000 armed rebels.
President Saleh has been a strong supporter of the US "war on terror"
Fighting broke out between rebel forces and government troops two weeks ago.
Since the 11 September 2001 attacks in the US, impoverished Yemen has launched a major crackdown against al-Qaeda sympathisers among the country's Sunni majority.
Mr Houthi has not been accused of links to al-Qaeda.
But anti-US and anti-Israeli sentiment is high all over Yemen because of the occupation of Iraq and the Israeli-Palestinian conflict.