Syrian troops and gunmen loyal to President Bashar al-Assad are reported to have stormed the town of Bdama near the Turkish border.
The alleged assault on Saturday followed another Friday of protests, which have grown in size despite Assad's wide-ranging military campaign to crush a three-month old uprising. Security forces shot dead 19 protesters on Friday, activists said.
"They came at 7:00am to Bdama. I counted nine tanks, 10 armoured carriers, 20 jeeps and 10 buses. I saw shabbiha [pro-Assad gunmen] setting fire to two houses," said Saria Hammouda, a lawyer living in the border town, in the Jisr al-Shughur region.
Bdama, about 20km from the Turkish border, has been a central location for the supply of food and other necessities to the thousands of people who have fled their homes and have taken shelter near the border.
"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," Rami Abdulrahman of the Syrian Observatory for Human Rights told the Reuters news agency.
On Sunday, Mustafa Osso, a Syrian rights activist, said that Syrian troops were tightening their grip on the city. He said that they had set up checkpoints and made dozens of arrests, implementing a strategy aimed at closing off the border and stopping the flow of refugees into Turkey.
Another activist said that security forces had torched a bakery in Bdama on Sunday, shooting one person in the stomach in the process. The man was evacuated to Turkey for treatment, the activist said.
A resident told AFP that Bdama was virtually deserted by Sunday morning.
Bdama is in the same region as Jisr al-Shughur, the focus of military operations a week ago.
Mohamed Fezu, a Syrian political activist, spoke to Al Jazeera from Jisr al-Shughur on Saturday afternoon and said: "We're surrounded by the military from all over the area."
Amid reports of Syrian troops moving into Turkish border towns, the British Foreign Commonwealth office issued a statement urging Britons to leave Syria "immediately" and advising against travel to Syria.
'Scorched earth campaign'
Tens of thousands rallied across Syria on Friday, defying state repression and ignoring a pledge that Assad's cousin Rami Makhlouf, a symbol of corruption among the elite, would renounce his business empire and channel his wealth to charity.
Witnesses and activists said that people rallied in the southern province of Deraa where the revolt began, as well as in the Kurdish northeast, the province of Deir al-Zor, and the city of Hama north of Damascus, the Mediterranean coast and suburbs of the capital itself.
The worst bloodshed on Friday was in Homs, a business hub of 1 million people in central Syria, where 10 demonstrators were killed, the Local Co-ordination Committees, a main activist group linked to protesters, said.
One protester was also reported killed in the northern commercial area of Aleppo, the first to die there in the unrest.
Nine people, including civilians and police, were killed in attacks by gunmen, the state news agency SANA said
Refugees from the northwestern region said troops and gunmen loyal to Assad known as "shabbiha" were pressing on with a scorched earth campaign in the hill farm area by burning crops, ransacking houses and shooting randomly.
Syrian rights groups say at least 1,300 civilians have been killed and 10,000 people detained since March.
Turkish officials told Al Jazeera on Sunday that 10,553 Syrians had currently been registered at "holding centres/camps", after having fled the violence in their country.
According to the Turkish authorities, 585 people arrived on Sunday, and 146 returned to Syria of their own free will.
The Turkish emergency agency said that it had begun to provide aid to refugees across the Syrian border, in addition to those in Turkish camps, on Sunday.