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.
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 numerous camps on the Syrian side of the border.
"This is a way of terrorising people," the man told BBC Arabic.
"Our group here is informing the world of what is going on inside Syria. [The authorities] don't like it, so they want to either arrest or kill these people, so that there are no more people who can follow the news from inside Syria. It is just terror for everybody."
Turkish mobilisation Syrian troops reportedly stormed Khirbet al-Jouz early on Thursday morning. Tanks and soldiers were seen on roads around the village, snipers were spotted on roof tops, and one witness saw a machine gun position being established.
A watchtower which had been flying a Turkish flag - put there by Syrians grateful for Turkey's help - was now flying a Syrian flag, witnesses said.
Villagers and journalists in Guvecci could see military activity across the border.
Umit Bektas, a Reuters photographer positioned on a hillside on the Turkish side of the border, said he had seen armoured vehicles taking up positions on the Syrian hillside, apparently with the aim of preventing more fleeing Syrians from reaching the camps next to the border.
Earlier on Thursday, hundreds of people broke through barbed wire to cross into Turkey, while another group of several hundred people were spotted further down the same road.
They were taken in more than 30 buses to refugee camps in Turkey, Bektas told the BBC Newshour programme.
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.
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.