"The United States government is not supporting Daesh," the embassy said in a terse statement, using another acronym for IS.
The United States "did not create or support Daesh in the past. Assertions the United States government is supporting Daesh are not true," it added.
The statement did not mention Erdogan by name but said there was "considerable misinformation circulating in Turkish media" about US operations against IS in Syria.
Erdogan had yesterday accused coalition forces led by the United States of supporting not just the Kurdish Peoples' Protection Units (YPG) in Syria but also IS.
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"It's quite clear, perfectly obvious," he said, adding that Turkey could provide proof in pictures and video.
The YPG works on the ground with the United States against IS but is seen as a terror group by Ankara and the local branch of the outlawed Kurdistan Workers Party (PKK).
However, the embassy said: "The United States government has not provided weapons or explosives to the YPG or the PKK -- period."
Responding to this allegation, the embassy said the United States continues to work closely with Turkey to "determine how we can increase our efforts to defeat (IS)... and eliminate this scourge that threatens both our peoples."
It said the discussions included how best to help Turkish forces and their Syrian opposition allies fighting the jihadists around Al-Bab.
The US backing of the YPG and criticism of the human rights climate in Turkey has angered Ankara in the final months of the administration of President Barack Obama.
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