Forces loyal to Libyan leader Muammar Gaddafi have shelled villages and towns to try to take control of the high ground in a western mountain range.

Rebel BelJassem, a citizen-turned-fighter from a village near Yafrin, said Gaddafi forces were using Grad missiles and rocket launchers in their nearly month-long siege, leaving residents trapped and cut off from food and medical supplies.

"We dig trenches and hide in there at night," says BelJassem, who gave only his first name for fear of reprisals.

Yafrin, which is 75 miles south west of Tripoli, is one of the biggest cities in the Nafusa mountain range, home to the ethnic Berber minority.

Medghamas Abu-Zakhar, a rebel based in Yafrin, said Gaddafi forces were shelling villages toward the top of the Nafusa range in an attempt to capture the high ground.

Yafrin is home to some 250,000 Berbers, said Fathi Abu-Zakhar, who is among the city's residents who fled the fighting. He said that two of his sons stayed behind.

"They are living under siege," he said. "No food and no medicine can get in. Even the injured have no way to get treatment since the only hospital has been shut down."

Further to the West, Libyan shelling forced the closure yesterday of the so-called Wazen passage, which is the route people fleeing Libya use to get to neighbouring Tunisia.

Jaber Naluti, a volunteer who has been trying to assist people in the area, said Gaddafi forces shelled the route, killing seven Libyan rebels. Some of the shells fell on the Tunisian side of the border.

Naluti said the shelling forced Tunisian authorities to close the passage.

Tunisian fighters flew over the area but did not fire.

The passage appeared to be functioning normally on today.

Gaddafi, who has ruled Libya for more than 40 years, has been using his military and militias to try to put down an uprising that began in February. The protests are aimed at ousting him from power.

The reports from Yafrin came a day after Nato said it would step up psychological warfare operations to try to persuade troops loyal to Gaddafi to abandon the fight.

Wing Commander Mike Bracken, speaking in Naples, Italy, said Nato planes have been dropping leaflets and broadcasting messages to Libyan forces urging them "to return to their barracks and homes".

He said the messages have also advised pro-regime troops "to move away from any military equipment" that could be targeted by Nato's strike aircraft.

He did not provide further details on the psychological operations. But the US has been using a specially-modified Air Force C-130 transport plane to broadcast messages to Libyan forces in AM, FM, high-frequency radio, TV and military communications bands.

Nato is operating under a UN Security Council mandate to maintain a no-fly zone and to take other actions to protect civilians from attack by Gaddafi's forces.

In recent days, Nato attacks have concentrated on military and logistics hubs in Tripoli.

There was no formal reaction from the Libyan government to reports that Shukri Ghanem, the Libyan oil minister and head of the National Oil Company, defected earlier this week and left the country for Tunis. The defection was confirmed by Abdel Moneim al-Houni, a former Libyan Arab League representative who was among the first wave of Libyan diplomats to defect.

Rebel forces have reported some gains in recent days. In Misrata, the main battleground in western Libya, opposition fighters claim they have driven back government troops from key access points and tried to push pro-Gaddafi gunners out of rocket range for the city.

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