Reports from Yemen say heavy fighting has broken out in the capital of Sanaa between security forces and members of the country's powerful Hashid tribe.
President Ali Abdullah Saleh himself belongs to the tribe, which has joined the opposition to his rule.
Several people were reported hurt in the clashes, which witnesses said involved machine guns and grenades.
The violence comes a day after Saleh refused to sign a deal to step down, prolonging the crisis in the country over demands by protesters that he end his nearly 33-year rule.
Saleh has been criticized by Western powers, in particular the United States and the European Union, for failing to agree to a transfer of power.
compiled from agency reports