"We shared our concerns about the U.S. giving armed weapons' training to members" of the PYD with the U.S. charge d'affaires Philip Kosnett, Turkish foreign ministry sources said.

The sources did not give any further detail.

While the U.S. views the Peoples' Protection Units (YPG) as the most effective fighting force on the ground against Islamic State (IS) extremists, Ankara calls it a "terrorist" organization linked to outlawed Kurdistan Workers’ Party (PKK).

Turkey claims both the YPG and the PYD are a branch of the Kurdistan Workers' Party (PKK), which is proscribed as a "terror" organization by Ankara, Washington and Brussels.

Relations between Washington and Ankara have been tense over multiple issues including a U.S. decision last year to deliver weapons to the YPG.

Reporter’s code: 50101