Forces loyal to Yemen's president Ali Abdullah Saleh have used helicopters and MiG fighter jets to attack bases of a rival tribal group, sources have told Al Jazeera.
Hakim Al Masmari, the editor of the Yemen Post, said on Friday the fighting was concentrated in the suburb of Nahem, north east of capital Sanaa, and that the air strikes started after the tribesmen belonging to the Hashid tribe attacked checkpoints around a Republic Guards camp, taking control of one of them.
Members of the Hashid tribe have joined the anti-government protesters in calling for Saleh to step down after he backed out of a deal brokered by the Gulf Co-operation Council (GCC) for him to peacefully step down.
Three months of street protests calling for an end to the 33-year rule of Saleh have brought the country to a near standstill.
"The tribes are very powerful, ruthless and well-armed," Al Masmari said.