Two U.S. officials told The Daily Beast that they had no intelligence identifying the perpetrators of Tuesday’s deadly terror attack at Atatürk Airport in Istanbul.

The two leading suspected groups are the self-proclaimed Islamic State (ISIS) and the Kurdistan Workers’ Party (PKK), a militant anti-Turkish government group seeking independence for Kurds in Turkey.

Privately, officials said they suspected ISIS, noting the PKK has historically not conducted these kinds of attacks on citizens, as such an indiscriminate attack would likely kill Kurds, breeding hostility, not a path toward self-determination. Roughly 20 percent of Turkey’s population is Kurdish.

And yet, while ISIS has been suspected in a number of bombings in Turkey, including the January attack on Istanbul’s Sultanahmet Square that killed 12, the terror group has never claimed responsibility for a bombing.

—Nancy A. Youssef