Turkey's National Security Council (MGK) said on Wednesday that the U.S. government's decision to arm the Syrian Kurdish YPG militia in Syria was "not befitting of an alliance".
"It has been stressed that the policy of supporting the PKK/PYD-YPG terrorist organization, acting under the guise of the Syrian Democratic Forces, by disregarding Turkey's expectation is not befitting of a friendship and alliance," the MGK said in a statement.
The United States said on Tuesday it started distributing arms to Syrian Kurdish militia battling to help retake the Syrian city of Raqqa from Islamic State, moving ahead with a war plan that has angered NATO ally Turkey.
Turkey views the YPG as an extension of the outlawed Kurdistan Workers Party (PKK), which has fought a three-decade insurgency in Turkey and is considered a terrorist group by the United States, Turkey and European Union.
The United States regards the YPG as a valuable partner in the fight against Islamic State militants in northern Syria.