Turkey regards the YPG militia as a terror group and a branch of the Kurdistan Workers Party (PKK) which has waged a deadly insurgency on Turkish soil for three decades.
Redur Xelil, head of foreign relations for the Syrian Democratic Forces, a US-backed alliance of fighters that includes the YPG, accused the Turkish forces of carrying out "demographic change" in Kurdish territory captured in Afrin, reported Reuters.
Although there have been pro-Kurdish demonstrations in Germany, Britain and France, the United Nations and Turkey's North Atlantic Treaty Organisation allies have done nothing to halt the Turkish offensive.
"We have got a little bit closer to Afrin". It said the area included some 90 villages to the west of Afrin city. Ankara has threatened to expand its current offensive in northern Syria to drive the Syrian Kurds out of Manbij. As lines blurred between the mainstream Syrian opposition and jihadis groups such as Al-Qaeda and the Islamic State militant group (ISIS), the US switched its focus from regime change to defeating ISIS via support for a mostly Kurdish coalition known as the Syrian Democratic Forces.
Europe's relations with Mr Erdogan has been fraught in recent years but the European Union depends on Turkey to keep a tight lid on immigration from the Middle East, where the war in Syria has killed hundreds of thousands and pushed millions from homes.
In its turn Turkey stated that the fighters had become Turkey's "legitimate target".
The operation has reportedly killed more than 1,100 civilians since it was launched in mid-February.
Turkey has explained that it is battling Kurdish "terrorists" to justify the offensive in Afrin, which has been largely untouched by Syria's deadly conflict until recently.
Turkey began drawing its military to the Syrian border in late June 2017.
Forces loyal to President Bashar al-Assad have meanwhile been pressing an assault to retake the opposition-held enclave of Eastern Ghouta, the last major rebel stronghold near to Damascus.