Local medics said 40 others were wounded after "the Gaddafi battalions" staged an attack on Zwara.
Informed sources said Zwara has come under the control of the pro-democracy protesters.
Several eastern cities have also fallen in the hands of the protesters during 10 days of revolution, which has reportedly claimed the lives of 1,000 people.
On Thursday, in the northwestern city of Misrata, protesters tore down Gaddafi's unique "Green Book" monument.
Libyans celebrated the liberation of the country's east from the rule of Gaddafi. Protesters set fire to a huge poster of Gaddafi in Zawiya.
The latest report said hundreds of soldiers have refused to shoot the pro-democracy protesters on the 10th day of nationwide rage against the Libyan dictator.
The news comes a day after an amateur video showed the bodies of some 130 soldiers slain because they refused to open fire on the protesters.
/106