Three more soldiers were injured in the "operation region", the defence ministry said in a statement after clashes with the militia on Thursday. It gave no further details.

Fighting broke out in several locations along the roughly 120-kilometre (75-mile) wide front where operations are focused, the Syrian Observatory for Human Rights and a Kurdish military official said Thursday.

Turkey Wednesday began an air and ground offensive supporting Syrian rebels against the US-backed Kurdish People's Protection Units (YPG) militia.

Ankara has long opposed US support for the YPG in the fight against the Islamic State extremist group, arguing the militia is a "terrorist" offshoot of Kurdish insurgents inside Turkey.

The ministry's statement comes after shelling from the militia into Turkey and Turkish military strikes in northern Syria, with casualties on both sides.

Seven civilians including a nine-month-old baby were killed in Turkish border towns in Sanliurfa and Mardin provinces. Nearly 70 were injured.

According to the UK-based Observatory, which relies on a network of sources in Syria, at least 29 fighters and 10 civilians have been killed in the war-ravaged country since the start of the assault.