Seven soldiers and several other people have been killed in clashes between the Yemeni army and Shi'ite Huthi rebels close to the capital, tribal and medical sources say.
The clashes erupted after troops tried to expel rebels from a strategic position near Amran controlling the road to Sanaa, local officials said.
The air force intervened to back the army and its allies from the Sunni Islah party, they said.
The rebels, known also as Ansarullah and backed by local tribes, retaliated by attacking telecom installations and blocked traffic on the main Amran-Sanaa road, the officials said.
"Seven soldiers were killed and 16 others wounded in the battle," a medical source said.
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Tribal sources said 18 rebels were also killed, a toll that could not be verified.
Rebel spokesman Mohammed Abdulsalam declined to give a death toll.
But he condemned the air force's intervention as a "very serious development" and warned of "consequences".
During the fighting, inmates escaped from an Amran jail, which came under rebel attack, the interior ministry said on its website.
A police source said that 10 Huthi rebels detained for "serious criminal charges" were among those who escaped.
Meanwhile in Sanaa, unknown gunmen opened fire on the home of Prime Minister Mohamed Basindawa, without causing injury, a security source said.
The rebels are suspected of trying to enlarge their sphere of influence as Yemen is split into six regions, pushing out from their mountain strongholds in the far north to areas closer to Sanaa.
The rebels complained Yemen would be divided into rich and poor regions under a federalisation plan agreed in February following talks as part of a political transition.
Huthis have been fighting the central government for years, complaining of marginalisation under ex-president Ali Abdullah Saleh, who was ousted in a 2012 uprising.
In February, they seized areas of Amran province in fighting with tribes that left more than 150 people dead.
