Heavy fighting erupted in and around the city of Taiz, located in central Yemen, Reuters has reported.
Residents said they saw fighting with an army brigade and tribesmen against Shiite Houthi militia and allied army units.
The Houthis have already been battling militiamen in southern Yemen. According to Reuters, this may signal that control over the army by the Houthi's ex-president Ali Abullah Saleh is weakening.
A Saudi-led coaltion has been bombing Yemen for over three weeks and has been concentrating on Houthi targets.
