Five protesters, including a schoolboy, have been killed in fresh bloodshed in Yemen as clashes between police and anti-regime demonstrations raged across the country.
Two doctors at the scene in Sanaa said that toxic gas, rather than ordinary tear gas had been used against the protesters yesterday, a claim dismissed as slander by the authorities.
Britain, the European Union and the United Nations condemned the crackdown.
Security forces in the impoverished country, a key US ally in the war against al-Qaeda, fired lived rounds and tear gas at demonstrators camping at University Square since February 21, killing one, protest organisers said.
More than 30 protesters were wounded by the gunfire, while and hundreds more suffered the effects of the tear gas, some passing out and others going into spasms, medics said.
A sniper shot dead another man as he walked with a group of demonstrators to the square, an opposition party member said.
Police shot dead the schoolboy in the southeastern city of Mukalla as they tried to disperse a student demonstration, witnesses and medics said.
And two other protesters were later killed in the southern port city of Aden: one by police when they opened fire to disperse a demonstration and the other when demonstrators set fire to a police station in the city.
A medical official said hundreds of angry people had set ablaze the police station to protest the death of the protester earlier in the day. Several people were also wounded by gunfire, he said
The violence comes a day after 14 protesters were wounded in protests across the country, which is already battling secessionist unrest, a Shiite sectarian rebellion and jihadists from al-Qaeda's Arabian Peninsula offshoot.
The dawn assault at Sanaa's University Square targeted demonstrators who had breached a concrete police barrier where activists have been staging a sit-in for almost three weeks, calling on President Ali Abdullah Saleh to step go.
Parts of Sanaa resembled a battleground as people passed out in the street and convulsed after inhaling gas fired at the demonstrators.