Hundreds of Syrian refugees are fleeing across the border into Turkey to escape an assault by Syrian troops in the area, witnesses say.
Tanks and snipers have entered the village of Khirbet al-Jouz - a base for makeshift refugee camps.
One group of people broke through barbed wire to cross the border close to the Turkish village of Guvecci.
More than 1,300 people are estimated to have been killed in the government crackdown on the popular uprising.
Thousands more protesters have been detained since the crackdown began in March, opposition activists say.
The recent military offensive in the north of the country 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.
Turkish mobilisation
Syrian troops reportedly stormed Khirbet al-Jouz early on Thursday morning. Tanks and soldiers were seen on roads around the village and snipers were spotted on roof tops.
A watchtower which had been flying a Turkish flag - put there by Syrians grateful for Turkey's help - is now flying a Syrian flag.
Villagers and journalists in Guvecci could see military activity across the border.
The AFP news agency said several hundred people broke through barbed wire to cross into Turkish territory, while another group of several hundred people were spotted further down the same road.
They are expected to join some 10,000 Syrians already taking refuge at tent cities erected by the Turkish Red Crescent in the border province of Hatay.
Meanwhile, Turkish forces have mobilised along the border.
The BBC's Jonathan Head in Istanbul says it is not clear how the Turkish government - increasingly critical of Syria - will respond to seeing troops harrying refugees who had assumed they were under de facto Turkish protection.
