Yemen security forces kill 12 protesters

"Twelve people have been shot dead by gunfire and 500 others were wounded by live rounds and batons or suffer from breathing difficulties due to inhaling tear gas," said Mohammed al-Abani, who heads a Sanaa field hospital.

Security forces and armed civilians opened fire on tens of thousands of protesters who left Change Square, where they have camped since February, and marched towards the centre of the capital, witnesses said.

Security forces also used water cannons and fired tear gas to disperse the rally, they added.

As clashes raged in the capital, massive demonstrations broke out in several cities south of Sanaa -- Taez, Yemen's second-largest city, Ibb, and Dhammar -- and in Saada in the north, to denounce the violence.

On Saturday, six university students were wounded in clashes between rival groups at Sanaa University, those involved and a medical official said.

Saleh is receiving medical treatment in Saudi Arabia following a June bomb blast on his presidential compound.

He has resisted regional and international calls for him to step down despite more than eight months of nationwide protests that have left at least 200 demonstrators dead across the country.

Copyright AFP (Agence France-Presse), 2011