A massive demonstration against Yemen's government turned into a killing field Friday as snipers methodically fired down on protesters from rooftops and police made a wall of fire with tires and gasoline, blocking a key escape route.
At least 46 people died, including some children, in an attack that marked a new level of brutality in President Ali Abdullah Saleh's crackdown on dissent. Medical officials and witnesses said hundreds were wounded.
The dramatic escalation in violence suggested Saleh was growing more fearful that the unprecedented street protests over the past month, set off by unrest across the Arab world, could unravel his 32-year grip on power in this volatile, impoverished and gun-saturated nation.
The United States, which has long relied on Saleh for help fighting terrorism, condemned the violence.
The bloodshed, however, failed to dislodge protesters from a large traffic circle they have dubbed "Taghyir Square" -- Arabic for "Change." Hours after the shooting, thousands demanding Saleh's ouster stood their ground, many of them hurling stones at security troops and braving live fire and tear gas.
They stormed several buildings where the snipers had taken position, dragging out 10 people -- including some the protesters claimed were paid thugs. They said the men would be handed over to judicial authorities.
The protest in the capital, Sanaa, drew tens of thousands, the largest crowd yet in Yemen's uprising. It began peacefully. A military helicopter flew low over the square just as protesters were arriving after the main Muslim prayer services of the week.
A short while later, gunfire rang out from rooftops and houses, sending the crowd into a panic. Dozens were hit and crumpled to the ground. One man ran for help cradling a young boy shot in the head.
Police used burning tires and gasoline to block demonstrators from fleeing down a main road leading to sensitive locations, including the president's residence.
"It is a massacre," said Mohammad al-Sabri, an opposition spokesman. "This is part of a criminal plan to kill off the protesters, and the president and his relatives are responsible for the bloodshed in Yemen today."
Witnesses said the snipers wore the beige uniforms of Yemen's elite forces and that others were plainclothes security officers. President Saleh denied at a news conference that government forces were involved, claiming that residents angry over the expanding protest camp had opened fire. He ordered the formation of a committee to investigate.
Doctors at a makeshift field hospital near the protest camp at Sanaa University confirmed at least 46 dead, three of them children. They spoke on condition of anonymity because they were not authorized to speak to the media.