Security forces in the Yemeni capital, Sanaa, have opened fire on tens of thousands of protesters demanding President Ali Abdullah Saleh's resignation.
Doctors and officials say at least nine people have been killed and many others wounded.
The protesters marching to the city centre were met with live rounds, tear gas and water canon, the BBC reports.
Witnesses in Sanaa said the demonstrators were marching from their stronghold in Change Square to an area controlled by the elite Republican Guard force, which is loyal to the president.
Mr Saleh has so far resisted calls from many Western countries to stand down, despite saying on several occasions he was prepared to do so.
In a separate development, the Yemeni defence ministry says a senior member of al-Qaeda has been killed during air raids in the south of the country.