GAZA (Reuters) - Dozens of people were killed and wounded Wednesday morning in an explosion in central Jisr al-Shughour in the northern Syrian province of Idlib, hours after fierce Russian air strikes, activists said.

Civil Defense elements said 17 people were killed and 35 wounded, most of them civilians, and medics said the death toll was high because of missing people under the rubble.

A number of buildings collapsed and several cars were damaged by the unknown explosion.

Residents spoke of a car explosion near a popular market without knowing if it was booby-trapped or less explosive, and others did not rule out that the powerful explosion was caused by a rocket.

Villages around Jisr al-Shughur saw attacks from Russian planes at night, and residents said long-range rockets hit the area from positions of the regime's army in nearby Lattakia.

Jisr al-Shughour and its environs have been the target of heavy shelling by the Russian air force and the regime's army for the last few weeks, resulting in most of the city's residents fleeing to safe areas near the Turkish border.

On September 17, Moscow and Ankara reached an agreement to establish a demilitarized zone in Idlib and its environs to protect it from an impending attack on the regime. Activists say Russia and the regime have committed dozens of violations of the Edelb scale reduction agreement.