US Defense Secretary Robert Gates (L) meets with Bahrain's King Hamad bin Isa Al-Khalifa at Sakhir Palace in Manama 12 March 2011. (AP)
Security forces in the impoverished country of Sanaa, Yemen, a key US ally in the war against Al-Qaeda, fired bullets and gas at demonstrators camping at University Square, killing one and wounding many more, protest organisers said.
Another protester was shot dead by a sniper in Sanaa as he headed with a group of other opposition partisans to the square, an opposition party member said.
"He was hit by a sniper shot," said the source, who requested anonymity.
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.
More than 30 protesters were shot with live rounds, while hundreds more suffered from injuries including loss of consciousness and spasms from breathing gases, medics said.
The dawn assault targeted demonstrators who had breached a concrete police barrier at University Square, where activists have been staging a sit-in for almost three weeks to demand democratic change.
President Ali Abdullah Saleh on Thursday offered to devolve power to parliament and pledged to protect protesters seeking an end to his three decades of iron-fisted rule.
The United States applauded the offer, with US President Barack Obama's top anti-terror advisor, John Brennan, on Friday calling on the Yemeni opposition to "respond constructively," according to a White House statement.
Opposition groups had already dismissed the promise of constitutional change and have vowed to escalate protests until Saleh, in power since 1978, resigns.
Parts of Sanaa resembled a battleground as people passed out in the street and convulsed with spasms after inhaling gas fired at the demonstrators.
"This isn't tear gas. This is poison gas that disables the nervous and respiratory systems. People hit by this gas pass out," said Iraqi doctor Hussein al-Joshaai, a nerve specialist who was at the scene.
Another doctor, Abdulwahab al-Inssi, said: "Those wounded today couldn't have been hit by tear gas grenades. They are suffering spasms."
The interior ministry denied the allegations as "baseless slander."
It accused protesters of opening fire at security forces who had tried to prevent clashes between protesters and residents near the square. It said 161 police had been injured.
The attack raged in the morning as security forces blocked all roads leading to the square and prevented ambulances from reaching the area to evacuate the casualties, protest organisers said.
A security official said police were not planning to storm the sit-in, only "return the demonstration to its size of yesterday because the expansion of the sit-in has disturbed residents."
US Ambassador Gerald M. Feierstein described Saturday's clashes as "dangerous".
"As the tension grows, as the positions of the two sides harden, the possibility for conflict grows. We consider this to be dangerous, we consider this not to be in the interest of the Yemeni people," he told journalists.
In other violence, police shot dead a 12-year-old schoolboy in the southeastern city of Mukalla as they tried to disperse a student demonstration, witnesses and medics said.
They also opened fire at students in Taez, south of Sanaa, wounding two people, a protest organiser said.
More than 30 people have been killed since the unrest began in late January, amid a tide of pro-democracy protests that have gripped the region and toppled autocratic regimes in Egypt and Tunisia.