The Turkish leader did not name any country, but Ankara has already accused Washington of “two-face behavior” in supporting Kurdish militia in Syria.
Speaking in the southern border city of Kilis on Saturday, Erdogan said some countries were backing the militants as part of their “dirty calculations” in the region.
Ankara and Washington have long been at loggerheads over the role of a US-backed Syrian Kurdish militia.
Turkey says the fighters are a terrorist organization affiliated with the outlawed Kurdistan Workers Party (PKK) but the US sees them as a partner in Syria operations.
Last month, Prime Minister Binali Yildirim said Turkey would not allow cooperation with terrorist organizations in Syria, referring to Kurdish groups which the US supports.
He said Turkey would not allow the formation of new states in Syria, echoing suspicion that the Kurdish campaign was aimed at establishing a separate state.
Turkey has been rocked by a series of bombings, including a deadly assault on Istanbul’s international airport which killed 45 people last week.
The attacks have prompted speculations that Turkey is facing a spillover of the Syria conflict.
Turkey stands accused of actively training and arming the Takfiri elements in Syria and facilitating their safe passage into the Arab country which has been gripped by foreign-sponsored militancy since March 2011.
In his Saturday remarks, Erdogan however accused Syrian President Bashar al-Assad who is fighting militants of being a “more advanced terrorist” than ISIS.
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