Many residents of eastern Syria's Al Bukamal city were arrested on Monday in a Syrian army assault, the Al Arabiya channel reported, citing eyewitnesses.
The city, near the border with Iraq, was stormed a day after President Bashar al-Assad said his regime was in no danger of falling and warned against a foreign intervention.
The troops also prepare to lay siege to another eastern city, Al Mayadin, and tanks are currently being deployed in the area.
Syria has been rocked by mass protests demanding reforms and the resignation of Assad for almost six months. Pressure from international powers has mounted to end the crackdown.
About 2,200 civilians are thought to have been killed since protests began in the southern city of Deraa in mid-March. According to government data, over 500 servicemen and security officers were also killed.
