Turkey does not think its efforts with the US to form a "safe zone" in north-east Syria will yield the results it wants and is ready to act on its own, Foreign Minister Mevlut Cavusoglu said on Thursday.
Ankara and Washington have agreed to establish a zone on the Syrian border that Turkey says should stretch 30 kilometres into Syria and be cleared of the Kurdish YPG militia, which it considers a terrorist organisation.
Turkey has accused the US, which supports the YPG-led force that defeated ISIS in Syria, of moving too slowly on the zone.
The two countries are also at odds over how far it should extend into Syria and who should control it.
Hulusi Akar, the Turkish Defence Minister, told US Defence Secretary Mark Esper that Ankara would end its work with the US if Washington stalled on the issue, his ministry said.
"Continuing to hold talks, wanting to solve the issue peacefully should not be viewed as weakness, and saying our plans are ready if necessary should not be seen as a threat," the ministry said Mr Akar told Mr Esper.
"If there is stalling or delaying, we are fully determined to end this work."
Turkey says it wants to settle up to 2 million Syrian refugees in the zone,
President Recep Tayyip Erdogan said on Tuesday that Turkey had no choice but to act alone given the lack of progress made with the US, in his most direct threat yet of a military incursion.
Speaking to broadcaster A Haber on Thursday, Mr Cavusoglu said the US did not seem to be sincere.