Erdogan's comments followed the release of the US Department of Defense's 2019 budget, which includes funds to train and equip the Syrian Democratic Forces in the fight against Daesh in Syria.
A decision by the United States to continue to fund the YPG/PKK will affect Turkey's decisions, President Recep Tayyip Erdogan said on Tuesday, ahead of a visit this week by Secretary of State Rex Tillerson.
In his remarks to the governing Justice and Development (AK) Party's parliamentary group in the capital Ankara, Erdogan called on the US to abide by its NATO obligations.
"What kind of NATO membership is this? What kind of NATO alliance is this?" he asked.
"As president of Turkey, [I say] NATO is not equal to the US, all countries [in the alliance] are equals to the US."
US officials have said that Tillerson expects to have difficult conversations when he visits Turkey on Thursday and Friday, given that the NATO allies have starkly diverging interests in Syria.
TRT World's Sara Firth has more from Kilis.
"Our ally's decision to give financial support to the YPG/PKK terror group ... will surely affect the decisions we will make," Erdogan said in a speech to members of his governing AK Party in parliament.
His comments followed the release of the US Department of Defense's 2019 budget, which includes funds to train and equip Syrian Democratic Forces - which is dominated by the YPG - in the fight against Daesh in Syria.
Turkey last month launched Operation Olive Branch in Syria to sweep the terror group from its southern border. It has also threatened to press on to the Syrian town of Manbij, under the control of a YPG/PKK terror group, and has warned American troops stationed there not to get in the way.
Turkey opposes any support to the YPG due to its links to the PKK, a group that is designated as a terrorist organisation by the US, the EU and Turkey.
Washington says it has no plans to withdraw its soldiers from Manbij and two US commanders visited the town last week to reinforce that message.
"It is very clear that those who say 'we will respond aggressively if you hit us' have never experienced an Ottoman slap," Erdogan said in parliament.
That was an apparent reference to comments made by the US Lieutenant General Paul Funk during a visit to Manbij.