Syrian unrest: 'Heavy fighting' in Jisr al-Shughour
Syrian government forces have advanced into the northern town of Jisr al-Shughour, state media say, as part of a widespread government crackdown.
TV reported heavy fighting with armed groups, two dead and large numbers of arrests, while witnesses reported an attack using tanks and helicopters.
The government says it is trying to restore order after 120 security personnel were killed last week.
Residents say they died after a mutiny and fighting between security forces.
The government advance sent more people fleeing towards the Turkish border, to join thousands who have already crossed.
BBC correspondents on the border say the number of those who have crossed is probably now much higher than the official figure of 4,300 given 24 hours ago. Witnesses said some 10,000 were sheltering in the area.
US officials say the government crackdown has created a humanitarian crisis, and called for the International Committee of the Red Cross (ICRC) to be given access to the north.
On the Turkish side, two camps are already full of refugees and a third is filling up rapidly.
There is a need for food and tents, but medical supplies are in particularly in demand to cope with large numbers of wounded.
The UN refugee agency has praised Turkey's response to the crisis but requested broader access to those in the camps.
The UNHCR said it considered anyone fleeing such a level of persecution to have the legal status of a refugee.
Turkish officials maintain that the displaced Syrians are not seeking refuge, as their eventual aim is to return home.
Activists and residents say troops began bombarding Jisr al-Shughour early on Sunday.
They then began to move in from the east and south in a two-pronged attack with 200 military vehicles, they said.
"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 TV said.
"Two members of the armed organisations were killed, large numbers of them arrested, and lethal weapons in their possession were seized."
The state news agency, Sana, said that after entering the town, army units had "cleansed the National Hospital of armed elements".
One resident told Reuters: "Tanks came from the south after shelling randomly and sending volleys of machinegun fire all over the town."
Helicopter gunships were also seen hovering overhead.
There are reports that the troops are from the army's fourth armoured division, which is commanded by President Bashar al-Assad's younger brother, Maher.
The BBC's Jim Muir in Beirut says there are also reports of members of the feared "Shabiha" militia group fighting alongside the soldiers.
It is not clear how much resistance the army is facing in the town, our correspondent adds, with so many people having fled.
"There are only a few people left. I escaped on my motorcycle through dirt tracks in the hills," one man told Reuters.
Syria has prevented most foreign journalists, including those from the BBC, from entering the country, making it difficult to independently verify reports from there.
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."
State media said two command groups of armed organisations had been detained, and others killed or wounded. Arms and ammunition were seized.
One account said some of those who tried to flee towards Turkey were intercepted, while others were shot and killed.
On Saturday, witnesses described homes being bulldozed in nearby villages and crops and fields burnt and uprooted.
Violence has also been reported in surrounding areas, including the town of Maarat al-Numan, where armed men are said to have attacked the courthouse, police station and strategic fuel depot.
Meanwhile, there are continuing but unverifiable reports of army defections, with the latest saying an officer and 50 men had changed sides rather than fire on civilians in Jisr al-Shughour.
Protests against President Assad, who succeeded his father Hafez in 2000, began in mid-March and have spread across the country. Rights groups say more than 1,200 people have been killed in the crackdown.