Yemeni security forces have killed at least 26 protesters taking part in a march in Sanaa.
More than 300 people have also been treated for gunshot wounds as they marched in the capital towards the presidential palace. Security forces opened fire with heavy weapons as tens of thousands of protesters called for President Ali Abdullah Saleh to step down.
Despite the violence, protesters vowed to continue to demonstrate.
Witnesses said that machine guns, anti-aircraft weapons, tear gas and water cannons were used on the crowds.
Saleh has been in Saudi Arabia since he was injured in an attack on his compound in early June.
State news agency Saba reported on 12 September that Saleh had authorised his deputy to negotiate a transfer of power with the opposition in an attempt to quell the violence.