Some of the first professional images to come out of Libya appear to show anti-Gaddafi rebels in control of the eastern city of Tobruk.
Soldiers said they no longer backed the Libyan leader and that the eastern region was out of his control.
They have been operating checkpoints and denouncing Gaddafi.
One general said he decided to switch sides after hearing the authorities had given orders to fire on civilians.
Tobruk lies close to the Egyptian border. Thousands have been fleeing across the frontier to make it home to Egypt and escape the violence.
In eastern Libya the military are now said to be mobilising to defend people against possible attack from Gaddafi’s forces.
Accounts say his supporters have been shooting people and a munitions store in Tobruk was bombed.