The US has expressed concern over reports that Syria is moving troops near the border with Turkey, and warned of a possible escalation of conflict.
Secretary of State Hillary Clinton said the reported Syrian troops movements were "very worrisome".
She said it could increase the risk of a border clash with Turkey and worsen the plight of refugees.
Syrian tanks and snipers reportedly entered the village of Khirbet al-Jouz, forcing residents to flee to Turkey.
More than 1,300 people are said to have been killed since a crackdown on anti-government protests began in March.
Thousands more protesters have been detained, opposition activists say.
Several Syrian cities - including Homs and Hama - have declared a general strike after deadly clashes with security forces and supporters of President Bashar al-Assad earlier this week.
"If true, that aggressive action will only exacerbate the already unstable refugee situation in Syria," Mrs Clinton said on Thursday evening.
"Unless the Syrian forces immediately end their attacks and their provocations that are not only now affecting their own citizens but (raising) the potential of border clashes, then we're going to see an escalation of conflict in the area."
Mrs Clinton also reiterated Washington's calls for President Assad to either implement promised reforms or resign.
"It is further example of the lengths to which President Assad's regime will go to repress the people of Syria rather than actually working in a collaborative way to try to resolve the legitimate concerns of the Syrian people."
The Syrian government's recent military offensive in the north of the country has forced thousands of Syrians to flee towards Turkey.
Many crossed the border, but a significant number opted to camp on the Syrian side of the border - preferring to remain on Syrian soil as long as possible.
One man said 2,130 people in his camp had fled Khirbet al-Jouz to avoid being attacked by the army, which was surrounding the camps on the Syrian side of the border.
"This is a way of terrorising people," the man told BBC Arabic.
Countering reports that thousands of Syrians were fleeing into Turkey, the Damascus government said on Thursday that more than 500 Syrians had returned to their homes. It also said they had been forced to flee by gunmen.
A BBC journalist who visited Khirbet al-Jouz at the weekend said the village was all but deserted by residents who anticipated the army moving in.
Troops moved into the village early on Thursday morning, according to eyewitnesses.
Residents and journalists in the Turkish village Guvecci said they could see military activity across the border.
Umit Bektas, a Reuters photographer positioned on a hillside on the Turkish side, said he had seen armoured vehicles taking up positions on the Syrian hillside, apparently with the aim of preventing more Syrians from reaching the camps next to the border.
Those fleeing were expected to join some 11,000 Syrians already taking refuge at tent cities erected by the Turkish Red Crescent in the border province of Hatay.
Turkish forces have mobilised along the border.
The BBC's Jonathan Head in Istanbul says it is not clear how the Turkish government - which has been increasingly critical of Syria - will respond to seeing troops harrying refugees who had assumed they were under de facto Turkish protection.
Syrian Foreign Minister Walid Muallem on Thursday called on Turkey to review its position, stressing that Ankara had always been a close ally of Damascus.
Syrian authorities also say they have eased restrictions to allow opposition figures to attend a conference in Damascus on Monday.
However, only independents - those not affiliated to opposition groups - will be allowed to attend. Signatories of the 2005 Damascus Declaration - a joint call for reform by Syria's most well-known intellectuals and dissidents - are barred.