Two of the soldiers were killed and three injured in direct fighting with the Syrian Kurdish People's Protection Units (YPG) militia in northeastern Syria, the defence ministry said.

The other two died after a shell hit a military base in Azaz further west, beyond the zone of the current offensive, according to state news agency Anadolu.

Turkey launched "Operation Peace Spring" on Wednesday against the YPG, which it considers a "terrorist" off-shoot of Kurdish insurgents in Turkey.

Violent clashes have taken place primarily around the Syrian border towns of Tal Abyad and Ras al-Ayn, which are controlled by the YPG.

The Syrian Observatory for Human Rights said 41 fighters for the YPG-led Syrian Democratic Forces have been killed since the operation began.

Kurdish forces have shelled Turkish border towns in response, killing a total of nine civilians on Thursday and Friday and injuring dozens more, according to the latest figures given by the government and local media.

Two of those civilian deaths occurred on Friday when a shell hit a house in the town of Suruc, adjacent to Kobane in Syria, Anadolu said.

Kobane was the site of a major months-long battle in 2014 and 2015 by Kurdish forces to retake the town from the Islamic State group.