Yemeni doctors say at least 31 people have been killed by security forces who opened fire on an anti-government demonstration in the Yemeni capital and that dozens have been wounded.

The death toll is among the highest in the month of violence that has shaken Yemen with protesters demanding President Ali Abdullah Saleh step down. Government forces and pro-government thugs have used live fire in an increasingly deadly crackdown.

Police started shooting at the protesters rallying outside the Sanaa University from rooftops and nearby houses as demonstrators filled the square after Friday prayers.

The two doctors who gave the toll spoke on condition of anonymity fearing reprisals. They work at a makeshift hospital at the protesters' encampment near Sanaa University, The Associated Press reports.