Istanbul
The Syrian Democratic Forces, the main US partner on the ground in Syria in the fight against Islamic State, includes the powerful Kurdish YPG militia.
Turkey views the YPG as an extension of the PKK militant group, which has waged a three-decade insurgency in Turkey and is considered a terrorist organisation by Ankara, the United States and the European Union.
"SDF confirms that it has no affiliation or ties to PKK," US Central Command said on Twitter, re-tweeting a statement by the SDF in which it said it was not part of the PKK and wanted a strong relationship with neighbours including Turkey.
"Is this a joke or @CENTCOM has lost its senses?" Erdogan's spokesman, Ibrahim Kalin, replied.
"Do you believe anyone will buy this? The US must stop trying to legitimize a terrorist group."
US support for the YPG has been a major sticking point between Washington and Turkey, a NATO ally and a member of the US-led coalition against Islamic State.
Turkey is hoping that the incoming US administration under President-elect Donald Trump will re-think its policy in Syria and stop providing support to Kurdish militia fighters.
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