Syrian tanks and helicopters stormed the town of Jisr Al-Shughour on Sunday, residents said, and state television reported heavy clashes between army troops and gunmen opposed to President Bashar Al-Assad.

More than 5,000 Syrian refugees have crossed the border and a UNHCR spokesman said the Red Crescent was preparing a fourth camp with room for 2,500 more. Witnesses said some 10,000 Syrians were sheltering near the border.

The assault on Jisr al-Shughour, astride a strategic road in northwest Syria, is the latest action by the armed forces to crush demands for political freedom and an end to oppression that pose an unprecedented challenge to Assad's 11-year rule.

Residents said earlier that most of the town's 50,000 people had fled towards the Turkish border about 20 kms away and tanks and helicopters were shelling and machinegunning the town.

Damascus has banned most foreign correspondents from the country, making it difficult to verify accounts of events.   

"Heavy confrontations are raging between army units and members of armed organisations taking up positions in the surroundings of Jisr al-Shughour and inside it," state television said.   

Army units defused bombs and explosive charges planted by gunmen on bridges and roads into the town, it said. "Two members of the armed organisations were killed, large numbers of them arrested, and lethal weapons in their possession were seized."    

State television said the forces uncovered mass graves of security men killed and buried by armed groups in Jisr al-Shughour and said their bodies bore marks of "atrocities". It did not give details.

The government said last week that "armed gangs" had killed more than 120 security personnel in the town after large demonstrations there. Refugees and rights groups said the dead were mutinous soldiers, shot for refusing to fire on civilians.

"When the massacre happened in Jisr Al-Shughour the army split, or they started fighting each other and blamed it on us," a woman refugee, who refused to give her name, told Turkish news channel NTV.

A senior Western diplomat in Damascus told Reuters: "The official version is improbable. Most people had left Jisr Al-Shughour after seeing the regime's scorched earth policy, shelling and the heavy use of armour in the valley."    

"The refugee exodus into Turkey is continuing and the numbers are higher than those officially counted so far."     

Asked if there were clashes in the town Mustapha, a 39-year-old mason who fled early on Sunday, told Reuters "What clashes? The army is shelling the town from tanks. Everyone has been fleeing.

"Even if we we did have guns, what are they going to do in front of artillery? Syria is a tightly controlled dictatorship and all of a sudden the regime says Jisr al-Shughour is armed to the teeth. They are lying. They are punishing us for wanting freedom."    

Residents said the army unit was commanded by Assad's brother Maher and was copying the tactics used in other centres to crush protesters demanding an end to Assad's autocratic rule.

The United States accused the Syrian government of creating a "humanitarian crisis" and called on it to halt its offensive and allow immediate access by the International Committee for the Red Cross to help refugees, detainees and the wounded.

Turkey has set up two large tented camps for refugees and sent the wounded to hospitals, but restricted access to the refugees, saying this is to protect their privacy.
 - Reuters