Shiite Huthi rebels clashed Monday with Yemeni army forces and loyalist tribes northeast of Sanaa as a UN envoy kept up mediation efforts, tribal sources said.
Fierce gunfights erupted when rebels attacked troops and armed tribesmen in the flashpoint Al-Ghayl district of Jawf province, tribal sources said.
The attack was in attempt to regain control of areas seized by the army, they said.
A tribal chief said scores of fighters were killed or wounded in the clashes, but AFP could not verify a death toll.
It was the latest escalation in a struggle to seize control of regions around the capital, including a main road linking Sanaa to Marib province in the east.
Analysts say the rebels are trying to establish themselves as the top political force in the northern highlands, bordering Saudi Arabia, where Shiites are the majority.
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Rebels have maintained protest camps in the capital for weeks as they pressure President Abdrabuh Mansur Hadi to sack the government and give them a greater say in power.
UN envoy Jamal Benomar held separate talks with representatives of the rebels and the government to mediate a deal that would end Yemen's political impasse.
The mediation comes after a potential deal was nearly reached last week, but it fell short due to lingering differences.
The rebels had earlier rejected an overture by Hadi in which he offered to name a new premier and reduced a controversial hike in fuel prices.
The rebels, also known as Ansarullah, had been demanding that Hadi consult them before naming a new prime minister.
Authorities want the rebels to dismantle their protest camps in Sanaa as part of a deal to resolve the crisis.
The rebels have battled the government for years from their Saada heartland in the remote north, complaining of marginalisation under former president Ali Abdullah Saleh.