Everything points to the latest attack being an act of terrorism by the separatist PKK and its Syrian Kurdish offshoot, the YPG. And while Washington is now shedding tears, it's the US that's supporting the supposed "freedom fighters" of the PKK/YPG in Syria with money and weapons, despite officially classifying the PKK as a terrorist organization. Through its policy of hypocrisy and double standards, the US shares responsibility for the innocent victims of the recent attack.
Although no one has yet claimed responsibility for the attack, Ankara is already spreading claims that the attack was masterminded by the Syrian PKK/YPG without providing any evidence. At the same time, it's accusing the US of being partly responsible through its alleged support of "terrorists" in Syria. The immediate spread of such theories presumably serves the purpose of justifying a renewed military campaign against US-backed forces in Syria.