Activists and a war monitoring group say Syrian government and Russian warplanes have targeted the southern edge of Idlib province with a series of airstrikes, ratcheting up the military pressure on the densely populated rebel-held bastion.

The intense air raids come a day after Iran and Russia backed a military campaign in the rebel-held area despite Turkey's pleas for a cease-fire. Turkey has troops and observations points that ring Idlib.

The Britain-based Syrian Observatory for Human Rights reported more than 30 air raids Saturday on a number of towns and villages in southwestern Idlib and adjacent northern Hama province, an area targeted over the last few days and that overlooks government-controlled areas.

Schools were shut in Khan Sheikhoun, an area under attack, because of the raids, the Observatory reported.