Hundreds of thousands took part in demonstrations in Sanaa, Yemen before security forces opened fire on the protesters gathered there.
The demonstrations had been held to reiterate calls for President Ali Abdullah Saleh to step down. Doctors said many were injured.
Many women took part in the protests, angry at President Saleh’s comments last week that their behaviour was against Islam.
More than 100 people have died in two months of protests against Mr Saleh, who has been in power for more than three decades.
He has said he is willing to hand over power, but only to “safe hands”.
An opposition delegation, led by former Foreign Minister Mohammed Basindwa, is meanwhile in Saudi Arabia for talks with Gulf Arab mediators.
In Sanaa, witnesses said that security forces opened fire with live ammunition and tear gas.
“We neared the Sanaa Trade Centre when police confronted us with tear gas, and suddenly opened heavy gunfire on us from all directions,” Sabry Mohammed, a protester, told Reuters news agency.
“A state of terror set in among the demonstrators, and some of them fled into side streets,” he added.
Mohammed al-Abahi, the head doctor at the protesters’ field hospital, told the Associated Press that at least 30 people were wounded, including two hit by bullets.
Protests were also reported in other cities, including Taiz, Aden and al-Hudaida.{jcomments on}