Turkish jets pounded US-backed Syrian Kurdish-led forces during the early hours of Oct. 20 in an apparent attempt to prevent them from establishing a long-coveted corridor to link up territories under their control in northern Syria. The Turkish attacks follow sustained threats from President Recep Tayyip Erdogan to take further action against the People’s Protection Units (YPG), which are closely linked to the Kurdistan Workers Party (PKK).

The airstrikes will likely further complicate Washington’s efforts to balance its relations with Turkey, a key NATO ally, and the YPG, which remains the US-led coalition’s most effective partner against the Islamic State (IS) in Syria. The YPG’s continued attempts to expand its territory in defiance of US warnings to stay put have not helped.

The Turkish army said that as many as 200 YPG militants were killed in the strikes, which targeted areas recently captured by the YPG as it continued its advance eastward toward the IS-held town of al-Bab. The YPG disputed these figures, claiming that no more than 10 fighters were killed. The London-based Syrian Observatory for Human Rights said 11 YPG fighters had died in the overnight sorties, which followed sustained Turkish artillery attacks against the Kurdish-controlled enclave of Afrin. There are conflicting reports as to whether the targeted group were YPG proper or a group affiliated with them.

Nilufer Koc, co-chair of the pro-PKK Kurdistan National Congress, said in an Oct. 20 statement that two villages had been shelled, killing four civilians and injuring dozens, “hours after their liberation from [IS].”