Two days of fighting between rebels and gunmen from the powerful Hashid tribes in north Yemen  have killed nearly 22 people, a tribal source said on Monday.
A presidential commission had on January 8 brokered a truce between the Houthi rebels  and Hashid fighters, ending two days of clashes in Amran province.
The fighting first erupted when Houthis tried to seize the towns of Wadi Khaywan and Usaimat, both Hashid strongholds.
But battles resumed a week ago and intensified over the past two days, the tribal source said, speaking to AFP.
"There were 22 people killed on both sides during the last 48 hours, " the source told AFP, adding that fighting was concentrated on Usaimat, 140 kilometers north of Sanaa.
The Houthis launched the attacks in retaliation for the Hashid tribe's support for hardline Salafist groups fighting Houthis in Dammaj, a rebel stronghold in the north.
The town in Saada province has been besieged by the rebels for months .
Houthi rebels have been battling the Sanaa government for nearly a decade in Saada, but the clashes with militants have deepened the sectarian dimension of the unrest.
Fighting that erupted in late October has centered on a Salafist mosque and Koranic school in Dammaj.
The conflict has spread in the northern provinces, embroiling tribes wary of the power of the Houthis , who have repeatedly been accused of receiving support from Iran.
Houthis, meanwhile, accuse radicals in Dammaj of turning the town center into "a real barracks for thousands of armed foreigners," a reference to the Dar al-Hadith Koranic school where foreigners study.
Yemeni troops began to deploy in Saada on January 11 to monitor a ceasefire between the Houthis and Salafists.