The Foreign Ministry Monday summoned U.S. Ambassador to Ankara Jeff Flake over a top U.S. military officer's visit to a U.S. base in the area dominated by the PKK's Syrian wing, the YPG, said diplomatic sources.

The sources said that the ministry sought an explanation for the visit.

Army General Mark Milley, Chairperson of the Joint Chiefs-of-Staff, made the unannounced visit Saturday to assess a nearly eight-year-old mission there and to review safeguards for U.S. troops against potential attacks.

About 900 U.S. troops are deployed in several bases and posts across northeastern Syria.

Similarly, the Syrian Foreign Ministry condemned the visit.

Official news agency SANA quoted a foreign ministry official as saying: "Syria strongly condemns the illegal visit of the American Chairperson of the Chiefs-of-Staff to an illegal American military base in northeast Syria."

Milley's visit was "a flagrant violation of the sovereignty and integrity," of Syrian territory, the official added according to SANA, calling on "the U.S. administration to immediately cease its systematic and continued violation of international law and support for separatist armed groups."

The PKK is a designated terrorist organization in the U.S., Türkiye and the European Union. Washington’s support for its Syrian affiliate, the YPG, has been a major strain on bilateral relations with Ankara.

The U.S. primarily partnered with the YPG in northeastern Syria to fight against the Daesh terrorist group. On the other hand, Türkiye strongly opposed the YPG terrorist group’s presence in northern Syria. Ankara has long objected to the U.S.’ support for the YPG, a group that poses a threat to Türkiye and terrorizes locals, destroying their homes and forcing them to flee.

Under the pretext of fighting Daesh, the U.S. has provided military training and given truckloads of military support to YPG terrorists, despite its NATO ally’s security concerns.