Ankara and Washington have long been at odds over Syria, where the United States has backed the YPG Kurdish militia in the fight against Islamic State insurgents. Turkey says the YPG is a terrorist organization and an extension of the outlawed Kurdistan Workers Party (PKK), which has waged an insurgency against the state in southeastern Turkey for 34 years. Turkey has already intervened to sweep YPG fighters from territory west of the Euphrates in military campaigns over the past two years, but up until now, it had not gone east of the river – partly to avoid direct confrontation with U.S. forces.
