AMMAN (Reuters) — Syrian opposition sources said Russian jets bombed rebel-held north-western Syria on Sunday in the most extensive strikes since a Turkish-Russian deal halted major fighting with a ceasefire nearly six months ago.

Witnesses said the warplanes struck the western outskirts of Idlib city and that there was heavy artillery shelling in the mountainous Jabal al Zawya region in southern Idlib from nearby Syrian army outposts. There were no immediate reports of casualties. Other tracking centres said Russian Sukhoi jets hit the Horsh area and Arab Said town, west of the city of Idlib. Unidentified drones also hit two rebel-held towns in the Sahel al-Ghab plain, west of Hama province.

There was no immediate comment from Moscow or the Syrian army.

Two witnesses said a Turkish military column comprising at least 15 armoured vehicles was seen overnight entering Syria through the Kafr Lusin border crossing in the direction of a main base in rural Idlib.