The commander of Syria's military police has defected from President Bashar al-Assad's government and reportedly fled to Turkey.
Lt Gen Abulaziz al-Shalal is one of the highest-ranking officials to join the uprising against the Syrian regime.
The army had failed to protect Syrians and turned into "gangs of murder", the general said in a video statement.
The announcement came amid reports of a deadly government strike in the northern province of Raqqa.
After reportedly crossing the border into Turkey, Gen Shalal released a statement saying he had defected because the military had perpetrated massacres in towns and villages instead of protecting Syrians.
"I declare my defection from the army because of its deviation from its fundamental mission to protect the nation and transformation into gangs of murder and destruction," he said in a video message posted online.
Opposition sources said the commander had been secretly co-operating with the rebels from the outset, the BBC's Middle East correspondent Jim Muir reports.
This is believed to be the case with many other senior defectors, our correspondent adds.
But Gen Shalal said defecting was becoming more difficult because of the increased level of surveillance
"Definitely, there are other high-ranking officers who want to defect but the situation is not suitable for them to declare defection," he said.
An unnamed Syrian security source confirmed the army chief's defection but played down its significance, Reuters news agency reports.
Gen Shalal was due to retire soon and joined the uprising to "play hero", the source is quoted as saying.
The US state department said it was not "in a position to confirm his actions or whereabouts".
"If true, this would be yet another sign of the regime crumbling from within, as those around Assad realise that the end of his rule is inevitable," spokesman Patrick Ventrell said.
"We continue to encourage regime officials and forces to
reject the horrific actions of the Assad regime. Syrian officials should
stand with the Syrian people." - BBC