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.

Rebels complain of socioeconomic and religious discrimination at the hands of the government. The government denies the accusations.

In the Harf Sufyan district, dozens of people died in three days of fighting between the rebels and tribesmen.

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 rebels of ambushing and killing a tribal chief, his son and four companions.

Rebels denied responsibility for the attack. Security officials said the tribal leader Zaidan Al-Maqnai was allied with Sanaa.

Rebels welcomed Qatar’s offer last week to mediate between them and Yemen.