The latest violence brings to about 300 the number of people killed in a month of fighting between government forces and supporters of an uprising, led by preacher and former MP Husain Badr al-Din al-Huthi.
"Almost 90 supporters of al-Huthi have been killed in violent battles with army forces over the past three days," said a military source on Sunday who was among the army troops in the mountainous area of Maran near the border with Saudi Arabia.
"Dozens were killed and wounded among the armed forces, who since Thursday have launched an offensive to take control of the last hideouts of al-Huthi, whose supporters continue to put up a tough resistance," the source said.
Yemen's president vowed his forces would stand their ground.
"We will never give up, whatever our sacrifices," Ali Abd Allah al-Salih said.
The president accused al-Huthi and his supporters of being "foreign agents", and made references to "foreign intelligence services" without identifying them.
President al-Salih vowed to go
after al-Huthi and not 'give up'
"The signs have started to become clear and they will be made public," said al-Salih, quoted by the state news agency Saba in comments marking 26 years of his presidency.
The president told Lebanon's Al-Mustaqbal newspaper in an interview earlier this month that "outside parties" were supporting al-Huthi's rebellion. "But we cannot point the finger at any country or party," he said.
Al-Salih had said the cleric was paying his supporters the "huge sum" of 18,000 Yemeni riyals or $100.
"Where does he get all this money? Who is the party financing him and to what end? We're leading an investigation into this but it's not possible that a local source is financing him," he told the daily.
'Prince of Believers'
Huthi, the self-styled Amir al-Muminin, or Prince of Believers, launched an uprising a month ago and is believed to be positioned in the rugged Maran area with as many as 3000 armed supporters.
According to residents, the army has been in control of an area known as Wadi Al-Futi since Friday, depriving the rebels of a key position used to supply them with logistics.
Al-Huthi is believed to have some
The protracted unrest, meanwhile, continued to force out inhabitants of the vast region.
More than 2000 families fled on Thursday and measures have been taken to supply them with food and shelter until military operations have ended, residents and aid workers told AFP.
A mediation effort last month led by MPs, including one of al-Huthi's brothers, to end the unrest was abandoned after the Zaidi preacher refused to surrender.
One of the MPs involved in the abortive effort, however, accused elements of the army of undermining efforts to resolve the crisis peacefully.
The authorities have offered a 10m Riyal ($55,000) reward for information leading to the capture of al-Huthi, whom they accuse of seeking to foment sectarian strife.
Al-Huthi heads the Faithful Youth organisation formed in 1997 as a breakaway from the Islamist opposition movement, Al-Haq.
The Zaidis are a Shia Muslim sect dominant in northwest Yemen, but in the minority in the mainly Sunni country.