The US has described as “ludicrous” a claim by Turkish President Recep Tayyip Erdogan that it supported so-called Islamic State (IS) in Syria.
State department spokesman Mark Toner said there was no basis for such an accusation.
The Turkish leader earlier said he had evidence that the US had supported the Kurdish YPG and PYD groups.
At least 37 Turkish troops have been killed during an operation launched in August to push IS militants and Kurdish fighters out of the area around Al-bab, a strategic town about 20 kilometre from the Turkish border.
The US has been working with the Kurdish groups in Syria but Turkey says they are linked to the Kurdistan Workers Party (PKK), which has been waging a decades-long insurgency inside Turkey.
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