The official said that heavy weapons and artillery were being used in the fighting in the northern city of Arman. Hawthi rebels, who belong to a branch of Shiite Islam, are fighting tribesmen from Yemen's largest tribal confederation, the Hashid, which is backed by an army unit and allied with the Muslim Brotherhood. Hawthis are backed by supporters from smaller tribes.
The number of casualties was not immediately clear but over the past months hundreds have been killed and injured in similar clashes that have spilled to northern cities where rebels accuse ultraconservative Salafis of trying to spread their ideology in Shiite strongholds.
The Hawthis waged a six-year insurgency in the north against ousted President Ali Abdullah Saleh, which officially ended in 2010.
Meanwhile, Yemeni officials accused Saleh and his loyalists of trying to stage a "coup" and roll back the country's transition from his rule.
Electricty went out across Yemen that day and lines of cars waiting for fuel stretched outside gas stations, amid reports of scattered demonstrations by armed men.
"This is aimed at bringing the wheel of history backward and taking us to square 1," Hadi said, without giving the names of those behind the alleged plot.