Troops meanwhile captured Jarajir, a town near Yabrud and on the Lebanese border, a military source told AFP on Wednesday. He denied the army had launched a new offensive, however, saying it was carrying out routine operations.

Amateur video distributed by activists showed plumes of black smoke rising above Yabrud, as a fighter jet soars through a clear blue sky.

The army last year launched a wide-scale operation to retake a string of towns in the area, seizing towns along the highway between Damascus and central Homs.

An activist who gave his name as Amer told AFP via the Internet that "the (army's) campaign to take Yabrud has started. The air strikes are accompanied by an attempted ground offensive."

The Syrian Observatory for Human Rights, a Britain-based group relying on a network of sources inside Syria, confirmed the escalation, saying Yabrud was hit by 20 air strikes Wednesday.

Located in the Qalamoun mountains, Yabrud lies near the Lebanese border and on the Damascus highway to the country's third largest city Homs, which has suffered some of Syria's worst fighting in the past three years.

Despite being under militant control, Yabrud was spared much of the violence engulfing most other opposition areas. Activists had for months considered it a haven for non-violent opposition to the government.

Syria has been gripped by deadly unrest since March 2011. According to reports, the Western powers and their regional allies -- especially Qatar, Saudi Arabia, and Turkey -- support the militants operating inside Syria.

More than 136,000 people have been killed in Syria's nearly three-year war, and millions more forced to flee their homes.

HH/HH