Street battles raged Thursday between the army and opposition tribesmen in the capital Sanaa and dozens of people on both sides were killed and wounded. Elsewhere a thousands-strong force of tribal fighters fought to break through government lines on the northern outskirts of the city.
Sanaa airport was closed Wednesday night and remains shut for fear that planes could be hit in the heavy shelling around the city.
The Defense Ministry issue a statement claiming the army stopped the tribesmen from entering Sanaa, but an army officer who defected from President Ali Abdullah Saleh's military, said the fighting continues.
A resident of Amran, who spoke on condition of anonymity for fear of government reprisal, said warplanes were breaking the sound barrier as they flew over that city and in the al-Azreqain area, where the tribesmen are battling their way toward the capital.
The defector army officer, who spoke on condition he not be named in accordance with opposition force custom, said the fighting was within 10 miles (15 kilometers) of the northern outskirts of Sanaa. He said the tribesmen had captured but later released 30 soldiers from the elite Republican Guard.
Heavy casualties were reported inside the city's Hassaba neighborhood where resident Talal Hazza said government troops were shelling opposition forces for a second day running. The army is trying to dislodge fighters loyal to pro-opposition Sheik Sadeq al-Amar.
The Defense Ministry acknowledge fighting in Hassaba for the first time Thursday. Opposition fighters have taken control of some government buildings in the region.
In the southern city of Taiz, three protesters were wounded in the fighting with the army, security men and plainclothes government enforcers, said activist Mohammed al-Darfi.
He said security forces stormed the house of Taiz opposition lawmaker Sultan al-Samie Wednesday night and confiscated his computer and documents.