Amid unremitting fighting in Syria that has claimed tens of thousands of casualties, another high-profile defection from President Bashar al-Assad's embattled government.

The army has failed to protect the country and has transformed "into gangs of killing and destruction," says the now former head of military police, General Abdelaziz Jassim al-Shalal.

In this video the senior officer blames the military for massacres against unarmed people.

A Syrian security source downplayed the significance of the defection, saying Shalal was due to retire in a month.

A number of senior military officials and soldiers have abandoned the bloody battle to crush rebel fighters, with some joining the opposition.

Footage of the conflict posted online cannot be independently verified by Reuters.

Shalal's announcement comes as government forces combat rebel advances around the country.