Medical officials in Yemen say more than 40 people have been killed in overnight street battles between government forces and rival tribal fighters in the capital, Sanaa.
Reports from the capital say fighting on the streets continues.
Clashes between tribesmen and security forces broke out in the city on May 31, shattering a truce announced four days earlier.
The fresh fighting comes a day after regime forces shot dead seven people demonstrating against President Ali Abdullah Saleh in Taiz, south of Sanaa.
Demonstrations demanding Saleh's resignation have been going on since the end of January.
compiled from agency reports