Turkish jets strike terrorist targets in Syria and Iraq's Sinjar region to prevent weapons and explosives from entering Turkey.
Turkish air strikes in northern Iraq and Syria targeted the PKK and YPG and were aimed at preventing them from setting up a base, President Recep Tayyip Erdogan said on Tuesday.
Erdogan said the strikes which killed 70, were intended to "drain the swamp" and prevent the PKK and YPG from smuggling weapons and explosives that could be used for attacks in Turkey.
The PKK is listed as a terrorist organisation by Turkey, the US, and EU, and it resumed its armed campaign against Turkey in July 2015. The YPG is the armed wing of the PYD, a Syrian affiliate of the PKK.
The president said Turkey will not let Sinjar become a PKK base and will continue military operations there and in northern Syria "until the last terrorist is eliminated."
Peshmerga fighters were also killed in the strikes and Erdogan said it was a "source of sadness."
The United States on Tuesday expressed "deep concern" over the air strikes. US State Department spokesman Mark Toner said that it had not been authorised by the US-led coalition, which is fighting Daesh in Iraq and Syria.
"These air strikes were not approved by the coalition and led to the unfortunate loss of life of our partner forces," Toner said.
Erdogan said local governments, the US and Russia, had been notified before the strikes.