Yemeni troops, backed by tanks and fighter aircraft, have launched a major offensive on the stronghold of Shia rebels in northern Yemen.
A second day of clashes on Wednesday came a day after the government vowed it would strike at the north's Houthi rebels with an "iron fist".
Government forces fired missiles on the headquarters of Abdul-Malik al-Houthi, the rebels' leader, in mountainous Saada province, tribal sources and rebels said.
Tribal sources told Al Jazeera that the army had launched air, artillery and missile attacks on the Malaheedh, Mahadher, Khafji and Hasama districts.
A statement from the Yemen's Supreme Security Committee said: "The state will strike these elements ... with an iron fist until they surrender themselves to justice."
The five-year-old battle between Yemen's Sunni-led governments against the Shia Muslim Houthi rebels is one of a widening series of conflicts threatening to destabilize the country.
'Repeated attacks'
Officials say the Houthi fighters, who belong to the Zaydi branch of Shia, want to restore a form of clerical rule prevalent until the 1960s in Yemen when it was overthrown in a military coup.
A government committee criticized the rebels for not abiding by an agreement to end hostilities announced by Ali Abdullah al-Saleh, the Yemeni president, in July 2008.
In comments published in the press on Monday, al-Saleh blamed the rebels for the flare-up of violence in the north, saying he was "pained by attacks undermining security, repeated attacks targeting civilians, vandalism".
But Mohammed Abdel-Salam, a spokesman for the rebels, was reported by The Associated Press as saying that the group is only fighting for improved living conditions and wants the Yemeni army out.
"We will continue the fight until the army is withdrawn from the province," he was quoted as saying.
"We are only defending ourselves."
Regional stability
Over the past few weeks, local officials say the rebels have taken control of more of Saada province from government forces.
Last week, they seized an important army post near Saada's provincial capital on a strategic highway linking the capital Sana with Saudi Arabia after 12 hours of intense combat.
They have also taken control of several more towns.
Local officials said on Tuesday that the rebels seized key army posts near al-Malahidh crossing, about 20km south of the Saudi border.
The stability of Yemen is a crucial concern for both Saudi Arabia, which shares a border with Yemen, and the US.
Riyadh fears the conflict could make the kingdom's own Shia tribes directly across the border more restive.
PHOTO CAPTION
A Yemeni soldier points to rubble in a building in 2007, which was damaged during months of fighting between rebels and the government in Saada province, 240 kms north of Sanaa.
Al-Jazeera