Clashes between Shi'ite rebels and pro-government tribes in north Yemen have killed 34 people over the past three days, local and security officials said, amid growing efforts to preserve a fragile truce in the area.
The violence comes after an offer from Qatar to revive a 2008 peace deal it brokered between the Yemeni government and northern rebels. The move was welcomed by both sides.
The truce was agreed in February to halt a war that has raged on and off since 2004, but instability still threatens Yemen, neighbour to top oil exporter Saudi Arabia, which was briefly drawn in to the conflict last year when rebels seized Saudi border areas.
Houthi rebels complain of socioeconomic and religious discrimination at the hands of the government. The government denies the accusations.
In the Harf Sufyan district, 28 people died in three days of fighting between the rebels, called Houthis after the name of their leaders' clan, and the government-allied Ibn Aziz tribe.
Rebels have clashed before over ideological differences with the Ibn Aziz tribe, which is from the same Zaidi sect of Shi'ite Islam to which the Houthis belong. This week's clashes appear to be the bloodiest since the start of the truce.
In a separate incident late on Tuesday, security officials accused Houthi rebels of ambushing and killing a tribal chief, his son and four companions.
The Houthis denied responsibility for the attack, which happened near the Saudi border. Security officials said the tribal leader Zaidan al-Maqnai was allied with Sanaa.
The Houthis welcomed Qatar's offer last week to mediate between them and Yemen.
In a statement on Monday, spokesman Mohammed Abdulsalam also justified the Houthi fighetrs' use of weapons, a violation of the ceasefire, saying that despite improved conditions, the Houthis were confronting heavily armed "war mongerers" in the region.
"The government must stop the aggression it has caused and it must stop stoking tribal conflict," Abdulsalam said.