More than 400 troops defected from the Yemeni military Saturday evening, saying they would no longer attack unarmed protesters, media reports said.
The troops announced their defection after standing for hours in front of tens of thousands of anti-government protesters in Sana'a and vowing to support their cause with their lives, Fars News reported.
"We will stand with the will of the people and will not kill unarmed youth. We are here to defend the people and we will do that," one soldier told CNN.
"The butcher must stand trial," the troops shouted as they marched in what has been known as Change Square Sana'a.
The organizing committee in the square announced this week that dozens of unarmed youth activists were killed by government forces over the past month. The committee says nearly 1,000 youths have been killed by the government since protests began in January.
Hours after the celebration, the defecting troops were welcomed at the military compound of Gen. Mohsen Ahmar, who defected from the government forces in March.
The majority of the troops were members of the Republican Guards and central security forces, which are headed by President Ali Abdullah Saleh's eldest son and nephew.
Youth activists celebrated the defection.
"With every day that passes, this oppressive regime is weakened," Abdul Nasser al-Kulaibi, a youth protester in Sana'a, told CNN. "Saleh will soon be surprised to see the rug beneath him pulled away and he will fall without expecting it."
He added, "Change will happen and we will not stop marching against the regime. More than 1,000 of us have died. It's too late to stop now."
Earlier in the day, state media reported that Saleh and senior government officials visited thousands of Republican Guard troops and encouraged them to stand firm in defending the country.
Saleh told the troops that Yemen's leaders are "willing to sacrifice for the sake of the country, but you will stay. You will remain here even if we let go of authority, because you are the authority," according to state media.
The country has been the scene of violent protests for months as people demand Saleh leave power after 33 years of dictatorship. Government troops have responded with live fire to protests, according to medics and opposition sources.
The guards number more than 80,000 and are considered the most powerful force in the country.
Saleh blasted the opposition forces and called them "gangs that cut off roads". He said those who have defected are part of the past.