Sanaa: Gunmen killed three protesters on Thursday taking the death toll to 19 in 24 hours of repression and prompting Washington to urge the beleaguered Yemeni President Ali Abdullah Saleh to agree "now" to a transfer of power.

Pro-Saleh gunmen on the roof of the ruling party's headquarters in Al-Bayda, 210 kilometres southeast of Sanaa, opened fire on demonstrators  tearing-up posters of Saleh, witnesses and protest organizers said.

In central Taez, Yemen's second-largest city, central security forces and units from the Republican Guard opened fire to disperse the latest protest in Jamal Street.

Dozens of protesters were wounded, said a medic at a field hospital in Freedom Square, the focal point of protests in Taez.

Thursday's crackdown came after a day of deadly protests.

In Sanaa, 12 people were killed and 340 wounded on Wednesday as security forces and plain-clothe gunmen fired at protesters marching from University Square towards the government headquarters, medics and witnesses said.

The interior ministry said protesters had attempted to break security cordons to "storm the radio (building) and government headquarters."

Besides gunfire and tear gas, security forces also used hot water on protesters at University Square, scalding at least 12 of them, a medic said.

Tension was mounting ahead of Friday rallies arranged by both sides as they have done since the start of the unrest.

Armoured troops led by dissident General Ali Mohsen al-Ahmar had put up a cordon around University Square, dubbed "Change Square" since protests began, to protect camping
protesters from a possible attack by loyal forces.