Rebel tanks fired at Tiji, where an estimated 500 government troops are stationed, and the blasts could be heard from the nearby town of Hawamid, which was captured on Thursday in a new offensive against the army.

"We have Tiji surrounded and we hope to take it by the end of the day," rebel commander Nasir al Hamdi, a former colonel in Gaddafi's police force, told Reuters as gunfire crackled in the distance and he surveyed a battleground scattered with tank shell casings and government anti-aircraft bullets.

Despite inferior firepower and little experience, rebels have captured several towns and villages where government forces had been dug in along plains below the Western Mountains this week.

Seizing Tiji would give the rebels a strategic and psychological boost, and could make it easier for the insurgents, who hold a chain of towns stretching more than 200 km across a bleak mountain plateau from the Tunisian border, to gain access to a key highway leading to Tripoli.

Insurgents in the Western Mountains, who are bitterly divided along ethnic lines, seemed to have improved coordination enough to work together in large numbers.

In the assault on Hawamid, for instance, hundreds of rebels in pickup trucks, backed by three tanks, sped down mountain roads towards the town and cut it off from government troops in other areas.

"It was very quick," explained Hamdi, standing on a dirt fortification where he said hundreds of government soldiers and militiamen had taken up positions.

Poor army morale may also have helped the rebels. Captured soldiers told Reuters earlier this week that officers had threatened them with death to force them to go to the front line in the Western Mountains.

Many of the soldiers fled Hawamid when the rebels advanced, ignoring graffiti scribbled by a soldier which said: "Capture the rats. Don't be afraid of them".

Gaddafi has said rebels fighting to end his four decades of rule were inspired by al Qaeda and has described them as rats in speeches.

The soldiers who were in Hawamid left behind boots, uniforms, food rations, blankets and underwear when they escaped in pick-up trucks to Tiji. Fifteen soldiers surrendered, Hamdi said.

"We questioned them. Gaddafi is forcing them to fight. Their heart isn't in this," he said.

Six months into the uprising the war remains deadlocked, and with the fasting month of Ramadan due to begin shortly, fighting may subside, so no major changes can be expected.

But rebel successes in the Western Mountain plains, where the rough desert terrain offers no hiding places from Gaddafi's missiles, seem to have raised spirits.

"We are not going to let up now even during Ramadan when we fast," said rebel Youssef Ali, standing beside tin foil plates filled with couscous and potatoes, the standard meal he and his comrades live on.