Syrian troops have stormed into a town near the border with Turkey, reports say, as the government presses its campaign to crush a popular revolt.
Witnesses and anti-government activists said tanks and soldiers swept into Bdama, making dozens of arrests.
Thousands of Syrian people have arrived in the border area over the past week, escaping military action in the north.
Turkey says some 10,000 have crossed over to its territory but many more are camping on the Syrian side.
The UK on Saturday advised against all travel to Syria and urged its nationals to leave as soon as possible.
Residents said the army moved into Bdama, about 2km (1.2 miles) from the Turkish border, early on Saturday morning, firing machine guns and setting fire to buildings.
"They came at 7am to Bdama," said Saria Hammouda, a lawyer living in the border town.
"I counted nine tanks, 10 armoured carriers, 20 jeeps and 10 buses. I saw shabbiha (pro-government fighters) setting fire to two houses," she added.
Activists say Bdama has become a vital supply point for the thousands of people who have fled their homes and are camped out near the Turkish border.
Rami Abdulrahman, of the Syrian Observatory for Human Rights, told Reuters: "Bdama's residents don't dare take bread to the refugees and the refugees are fearful of arrests if they go into Bdama for food."
Bdama is in the same region as the town of Jisr al-Shughour, where a recent army campaign restored government control.
The army said it was pursuing "armed groups" who had seized Jisr al-Shughour and killed more than 100 security personnel. Other reports said there had been a mutiny among security forces in the town.
The authorities have called on people who fled the fighting to return home, but the town is reported to be almost deserted.
On Saturday, Turkey for the first time allowed journalists into a refugee camp for people who have fled neighbouring Syria in the last two weeks.
Some refugees spoke of detentions, torture and beatings by Syrian troops.
An elderly refugee who gave his name as Adem told Reuters news agency: "They passed electricity through our toes. I was tortured, too. They asked for the names of people who had participated in the demonstrations."
President Bashar al-Assad is facing the gravest threat to his family's 40-year rule, as unrest that first erupted in March in the south of the country has now engulfed the north and threatens to spread east towards Syria's border with Iraq.
The government crackdown has brought widespread international condemnation.
US Secretary of State Hillary Clinton, writing in the pan-Arab London-based Asharq al-Awsat newspaper on Saturday, said military action would not quell the momentum for change in Syria.
The regime's "continued brutality may allow [President Assad] to delay the change that is under way in Syria, it will not reverse it," she wrote.
The UN says that at least 1,100 people have died since protests began, but Syrian rights groups put the overall death toll in Syria at 1,297 civilians and 340 security force members.
Syria has prevented foreign journalists, including those from the BBC, from entering the country, making it difficult to independently verify reports from there.
Activists and witnesses said security forces had opened fire on demonstrators in several locations on Friday, killing at least 19 people.