Turkish warplanes have carried out airstrikes on Kurdish Workers' Party (PKK) militants near Iraq's Sinjar mountains and in northeastern Syria, a statement from the military said on Tuesday.
The statement said the strikes were aimed at preventing the outlawed group from sending weapons, explosives and fighters for attacks inside Turkey.
"To destroy these terror hubs which threaten the security, unity and integrity of our country and our nation and as part of our rights based on international law, airstrikes have been carried out ... and terrorist targets have been struck with success," the statement said.
The operations were carried out in the early hours of Tuesday morning, it added, but gave no details of casualties.
Howevever, the British-based Syrian Observatory for Human Rights, which is monitoring the Syrian conflict, said at least 18 Kurdish fighters and media officials from The People's Protection Units (YPG) were killed when Turkish warplanes hit a media center. Turkey considers the YPG, which is backed by the US, as an extension of the PKK.
The Observatory bases its reports on information gathered from a network of activists on the ground in Syria.
In Iraq, Kurdish sources said that six Iraqi-Kurdish Peshmerga fighters were killed by accident during a Turkish strike on a nearby PKK position.
In a statement, Iraq's autonomous Kurdistan region said the Turkish airstrikes on the peshmerga were "unacceptable," but that the apparent accident should be blamed on the PKK, whose affiliates were the target of the strikes.
Turkish President Recep Tayyip Erdogan has long said that the Sinjar region, some 115 km (71 miles) from the Turkish border, is becoming a hotbed for PKK militants, and that Ankara would take measures to stop the group expanding its activities there.
Although Turkey regularly carries out airstrikes against what it says are PKK targets in northern Iraq, this was the first time it has struck the Sinjar region.
The PKK, which has waged an insurgency for Kurdish autonomy against the Turkish state for three decades, has been classified as a terrorist group not only by Ankara, but also by the European Union and the United States. The conflict has claimed more than 40,000 lives.