The PKK is the Kurdistan Workers' Party, a militant group that has waged a separatist campaign for more than 30 years.
It would have been a brutally cynical act for the PKK to attack a peace rally attended by Kurds. Most of the victims of Friday's bombings were attending a lunchtime demonstration calling for an end to the renewed conflict between the PKK and the Turkish government. Those taking part included the pro-Kurdish HDP, or Peoples' Democratic Party, which said on Twitter two of its parliamentary candidates were killed in the blasts.
Davutoglu has said recently that would-be suicide bombers have been arrested crossing into Turkey from Iraq, where the PKK has bases. ISIS does not control any part of Iraq's border with Turkey, though it does have access to parts of Syria's border with Turkey.
The Turkish military has conducted airstrikes in recent months against suspected PKK targets in the mountains of northern Iraq.
Kurdish forces have been battling ISIS jihadists across a swath of northern Iraq and Turkey.