President Recep Tayyip Erdoğan said late Tuesday that he rejected a demand by his U.S. counterpart Donald Trump regarding Turkey's ongoing anti-terror operation in northern Syria.

"Mr. President demanded that we declare a ceasefire. We never will," he said, reiterating that Turkey ruled out any negotiations with terrorists.

"No ceasefire is possible in Syria until the People's Protection Units (YPG) evacuates the border area," he said, adding: "I told him that Turkey will not negotiate with terrorists."

Erdoğan said the aim of Operation Peace Spring was for the YPG to move beyond 32 km (20 miles) into Syria.

Regarding the key town of Manbij, Erdoğan said that terrorists should not remain there.

"The Assad regime entering Manbij is not (a) very negative (development), but the YPG must get out," Erdoğan said. However, he added that talks with U.S. and Russian on Manbij and Ayn Al-Arab (Kobani) continued.

On the topic of sanctions, Erdoğan was unfazed. He said Turkey was not worried about sanctions.

Erdoğan's comments come a day after the U.S. announced sanctions on two Turkish ministries and three senior government officials over Turkey's anti-terror operation in northeastern Syria.

Turkey launched Operation Peace Spring, the third in a series of cross-border anti-terror operations in northern Syria targeting terrorists affiliated with Daesh and the PKK's Syrian offshoot the YPG, on Oct. 9.

The operation, conducted in line with the country's right to self-defense borne out of international law and U.N. Security Council resolutions, aims to establish a terror-free safe zone for Syrians return in the area east of the Euphrates River controlled by the U.S.-backed Syrian Democratic Forces (SDF), which is dominated by YPG terrorists.

The PKK — listed as a terrorist organization by Turkey, the U.S. and the European Union — has waged a terror campaign against Turkey for more than 30 years, resulting in the deaths of nearly 40,000 people, including women, children and infants.

The Turkish president also touched upon another point of contention with the U.S.: the F-35 stealth fighter jets.

Alternatives for the F-35s are ready and "offers are coming in", Erdoğan said.

Ankara and Washington have clashed over Turkey's purchase of Russian S-400 missile defenses, which the United States says are not compatible with NATO defenses and pose a threat to Lockheed Martin Corp's F-35 stealth jets.

Washington removed Turkey from the joint F-35 program after it took delivery of the S-400 systems in July. Ankara, a buyer and producer of the jets, has said it could look elsewhere.