The renewed violence comes despite efforts to implement a peace deal between the government and the fighters, brokered by Qatar.
Thousand of people have been killed since a 2004 uprising in Saada by members of the Zaidi community, a branch of Shia Islam.
The fighters, known as Huthis after Hussein Badr Eddin al-Huthi, their former commander who was killed by the Yemeni army in September 2004, have been battling to restore the Zaidi imamate which was overthrown in a coup in 1962.
Tribal leaders in the northern region of Yemen, a predominantly Sunni country, say more than 30,000 residents have been displaced by the fighting.