Turkey’s President Recep Tayyip Erdogan on Tuesday pledged to consider U.S. President Donald Trump’s proposal to establish a safe zone in northeastern Syria ahead of a planned Turkish offensive against the U.S.-allied Kurdish fighters who control the region.

Erdogan conditioned setting up the safe zone on clearing the area of the U.S.-backed Kurdish People’s Protection Units (YPG/YPJ), who Ankara believes are affiliated with the Kurdistan Worker’s Party (PKK) communist terrorist group, Hurriyet Daily News reports.

“Mr. Trump once again confirmed his decision to withdraw from Syria. He also spoke about a security zone more than 30 kilometers [about 18 miles] deep inside [Syria], which would be set up by us, an issue that I had raised during the Obama administration,” Erdogan declared during his weekly address to Turkish lawmakers on Tuesday in Ankara, Hurriyet notes.

“We had suggested securing the ground if the U.S. would provide aerial protection. [Former U.S. President Barack] Obama did not take the necessary steps on it although he was in favor of it,” he added.

The Turkish president explained that safe zone negotiations between the United States and Turkey were still needed to define what logistics the U.S. and its coalition partners will provide for securing the territory and reconstructing the area after the return of Syrian refugees.

“We can be involved in this with our TOKİ [Turkey’s urban development agency]. But if financial support would be provided by our coalition partners, we can establish this secure zone and provide security for all these people. This would also stop migration,” Erdogan noted.

For months, the Turkish military has been preparing to launch an operation against fighters from the YPG, the armed wing of the Kurdish Democratic Union Party (PYD) that has maintained control over most of northern Syria with the help of U.S. troops fighting the Islamic State (ISIS/ISIL) in the area.

Referring to the safe zone, Erdogan said, “Can the YPG take part in such a project? They are terrorists. Can we leave this area to the terrorists? For us, there is no difference between [ISIS] and the YPG/PYD.”

Although Ankara has long accused the YPG of being affiliated to PKK terrorists, the United States continues to provide support to the Kurdish fighters, arguing that they are the most effective force against ISIS.

News of the potential safe zone for Kurds came days after Trump, via Twitter, threatened to “devastate Turkey economically” if Turkish forces attack the Kurds in Syria after the United States’ planned withdrawal.

“This tweet has saddened us. Why? Because we are strategic partners. We may have different positions on some issues, but we should be locked on the same objectives,” Erdogan said on Tuesday, referring to the American president’s remarks.

In responding to the tweet, the Erdogan administration also said it would be a “fatal mistake” to consider Ankara’s operation against the YPG, an attack against all Kurds, separating the militia group from the predominantly Kurdish population in northern Syria.

Trump revisited the notion in his tweet of establishing a security zone inside Syria to address Ankara’s Kurdish-linked security concerns.

U.S. National Security Adviser John Bolton recently said America’s withdrawal from Syria would be contingent upon assurances from Turkey that the Kurds will be safe, which Ankara failed to provide. However, it appears Erdogan has changed his mind.

In the wake of Trump’s tweet threatening Turkey over the Kurds, the U.S. leader spoke to Erdogan on Monday to discuss the recent developments.

Citing a read out by the Turkish presidency, Hurriyet notes that the leaders “discussed the idea of forming a terror-free safe zone in the north of Syria by Syria’s territorial integrity.”

“We have decided to take comprehensive and speedy steps to increase our trade volume to $75 billion. Therefore, we could strengthen our joint perspective in spreading the positive spirit on our ties over Syria to the economic sphere as well,” Erdogan reportedly said on Tuesday, referring to the call.

President Trump has announced plans to pull out American troops from Syria, but Bolton indicated a residual force would remain in the country to combat Iran’s growing influence.