Turkey considers the YPG to be the Syrian branch of the Kurdistan Workers’ Party (PKK), which it considers a terrorist organization.
The PKK began an insurgency against Ankara over 40 years ago for Kurdish rights and autonomy.
Turkey and Syrian extremist militias it backs are alleged to have committed war crimes during the October assault on the Kurdish-led region.
After the US abandoned its long-time ally in the fight against the so-called Islamic State, the SDF turned to Russia and the Syrian government, with which it avoided confrontations since the start of the Syrian conflict.
Moscow then sat at the negotiating table with Ankara, offering parts of the border areas to it as the Syrian government takes the rest, and the SDF retreats.
This was on guarantees that Turkish operations would cease.
The SDF has repeatedly stated that Ankara continues attacks as the latter claims the former is yet to retreat fully.
After US troops left, effectively greenlighting the Turkish attack, they have now sent reinforcements to oil fields in Deir al-Zor province, also controlled by the SDF.
Editing by Karzan Sulaivany