US Secretary of State Hillary Clinton has said that her country is concerned by reports that Syria is massing troops near the border with Turkey, which could escalate the crisis in the region, and is discussing the issue with Turkish officials.
Clinton said the reported move by Syria to surround and target the town of Khirbet al-Jouz just 500 metres from the Turkish border marked a worrying new phase of Syria's attempt to quash anti-government protests.
"If true, that aggressive action will only exacerbate the already unstable refugee situation in Syria," Clinton said late on Thursday.
"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."
Clinton said she had discussed the situation with Turkish Foreign Minister Ahmet Davutoglu and that President Barack Obama had also talked to Turkish Prime Minister Tayyip Erdogan.
Meanwhile, the European Union is preparing a draft statement questioning the legitimacy of Syria's leaders, expected to be released on Friday.
Syrian troops gathered near the Turkish border, witnesses said on Thursday, raising tensions with Ankara as President Bashar al-Assad increases the use of military force against a three-month-old popular revolt.
Turkey said the two countries' foreign ministers had consulted by telephone, and Syria's ambassador to Ankara was later summoned to the foreign ministry, demonstrating further how disturbed Turkey is over events in its southeast neighbour.
According to the witness accounts, soldiers drove through the village of Khirbet al-Jouz on Thursday. There were also unconfirmed reports that forces were firing machine guns randomly in the nearby village of Managh.
Syrian armoured personnel carriers were visible on a road running along the top of a hill, and machine-gun fire was heard although it was not clear who the troops were firing at.
Speaking to Al Jazeera by phone from Khirbet al-Jouz, Mohamed Fezo, a witness, said: "At 6:30 in the morning about 30 tanks and several buses carrying thugs and intelligence operatives attacked Khirbet al-Jouz. They opened fire randomly across the village.
In-depth coverage of escalating violence across Syria
"Most of the villages population has escaped to the Turkish border expecting the village to be attacked. When the army did attack, the people escaped to Turkey, around 2,000 of them. The only people who remained in the village were the elderly who couldn't escape. We have received confirmed reports that some of these men have been arrested."
The Turkish Red Crescent said 600 refugees crossed from over Syria to escape the latest assault.
Al Jazeera's Anita McNaught, reporting from the Turkish border village of Guvecci, said that she could see Syrian soldiers from where she was.
"We can see soldiers and armoured trucks just across the border, within view from this refugee camp that we're in," she said.
"We were told at 6:30 this morning, that people here received calls from Syria saying that Syrian troops had moved in with tanks and armoured vehicles and they were clearing the village out."
Buses for refugees
Our correspondent said a building in Syrian territory on which a Turkish flag could be seen earlier, was now carrying a Syrian flag and had snipers based on the roof.
"We can see men carrying rifles standing on the building and we're being told that those are snipers up there, on patrol," she said.
She said though Turkey had not issued any official statement, the authorities did bring in buses for those refugees who wanted to evacuate the border area.
Several hundred people broke through the barbed wire marking the frontier between the two countries and were seen advancing into Turkish territory on a road used by Turkish border guards, a few kilometres from Guvecci.
They were flanked by Turkish paramilitary police vehicles and minibuses, called apparently to ferry the refugees to tent cities the Turkish Red Crescent has erected in the border province of Hatay.
Another group of several hundred people was seen further down the same road, walking towards the Turkish security forces' vehicles.
At the weekend, the Turkish Red Crescent announced it had begun providing urgent humanitarian aid to those massed on the other side of the border.
More than 1,300 civilians have been killed and some 10,000 people arrested, according to Syrian human rights groups, in the crackdown that has seen troops dispatched to crush pro-democracy protests across Syria since March.