It said that 25 "terrorist members" of the Turkey-based Kurdistan Workers Party (PKK) and the Syrian Democratic Union Party (PYD) had been killed in the strikes in the area of the Syrian town of Jarabulus and five buildings used by them destroyed.

A monitor said earlier that Turkish shelling and air strikes killed at least 35 Syrians, in the first reported civilian casualties in Turkey's intensifying campaign in northern Syria.

The army said it was doing everything to avoid civilian casualties.

"All possible measures are being taken to prevent harm to the civilian population living in the area and the maximum sensitivity is being shown on this issue," the army said, quoted by Anadolu.

Turkey classifies the PKK and PYD as terror groups but while the United States sees the PKK as a terror group, it supports the PYD's People's Protection Units (YPG) militia as an effective adversary of the Islamic State (IS) group.

The Turkish army on Wednesday launched a two-pronged cross-border offensive against both IS and the Syrian Kurdish fighters, sending in dozens of tanks and hundreds of troops.

Within hours of the start of the operation, Turkey-backed rebels had routed IS from Jarabulus.