Rebels seized a prison outside the city where Syria's uprising began three years ago this month and freed dozens of inmates, activists said on Wednesday.

They took control of the Gharaz Central Prison on the outskirts of Deraa near Syria's border with Jordan after fighting off President Bashar Assad's forces.

Rebel supporters posted videos online showing what they said were fighters touring the prison grounds and greeting and embracing prisoners they had freed.

"God give life to the Free Syrian Army," men chanted in one video, referring to anti-Assad rebel fighters. Another video showed four bodies of what were said to be pro-Assad soldiers. "This is the fate of all tyrants," the man filming said.

Rami Abdulrahman, head of the Britain-based monitoring group the Syrian Observatory for Human Rights, said more than 300 people had been held in the prison but it was not clear how many had been freed on Wednesday, although videos showed dozens.

The prison had held inmates who were arrested at protests, he said. But it was not immediately clear how many of those freed were political prisoners.

Fighting for the prison had gone on for more than 50 days before rebels took it Wednesday morning, and six rebel fighters had been killed in the fighting yesterday, Abdulrahman said.

Elsewhere, insurgents have suffered a series of losses to Assad's forces along the Lebanese border to the north.

On Wednesday, the town of Ras al-Ain fell to government forces after the capture on Sunday of Yabroud, which rebels had used as a conduit for arms and supplies from Lebanon.

More than 140,000 people have been killed in the conflict, which started as a peaceful call for reforms but turned full-scale civil war after a government crackdown on protests.