Soldiers are reported to have fought defectors in one of the biggest battles yet of Syria's nine-month uprising against President Bashar al-Assad.
Reports said government troops entered the town of Busra al-Harir near the border with Jordan early on December 11.
Reuters says explosions and heavy machine-guns were heard there and in nearby Lujah.
There was no word on casualties.
Meanwhile, opposition activists said they had shut down much of the capital Damascus and other towns with a strike.
The opposition stronghold of Homs and its countryside were mostly shut down by the strike. Elsewhere, the impact was difficult to gauge.
The Syrian Observatory for Human Rights said security forces had forced shopkeepers to keep shops open in some neighborhoods on the outskirts of Damascus. This could not be independently confirmed.
The official news agency SANA said 13 soldiers killed by "armed terrorist groups" were buried on December 11.
Elsewhere, France's Foreign Minister Alain Juppe said Paris believed Syria was behind attacks that wounded French peacekeepers in neighboring Lebanon on December 9.
Meanwhile, Syria is holding municipal elections amid the continuing violence, with nearly 43,000 candidates contesting over 17,000 seats in local councils across the country.
Voter turnout is expected to be low, as the opposition has called for a boycott of the election and also many voters are unlikely to risk going out to vote amid the violence.
The United Nations says more than 4,000 Syrians have been killed since March. Assad says the number of dead is far lower and most of them have been from the state security forces.
compiled from agency reports