ISTANBUL (Reuters) - One Turkish soldier was killed and another was wounded in a mortar attack on their position in northwest Syria on Sunday and Turkey’s military launched retaliatory fire, the Turkish Defense Ministry said.

It said the attack was carried out by the Kurdish YPG militia in the Afrin region, where Turkey-backed Syrian rebels drove out YPG fighters last year.

Ankara says the YPG is a terrorist group and an extension of the outlawed Kurdistan Workers Party (PKK) which has waged an insurgency on Turkish soil since 1984.

“After the incident, targets identified as belonging to terrorists were subject to fire,” the ministry said in a statement.

The ministry published a photo of the soldier who was killed on its Twitter feed.

The YPG militia has been a key ally of the United States in its fight against Islamic State in Syria.