WASHINGTON -- A senior U.S. diplomat on December 13 held talks with officials in Bratislava and attended the signing of an agreement under which Slovakia is to buy 14 F-16 military jets from Lockheed Martin as it seeks to replace Soviet-era jets.

Deputy Secretary of State John J. Sullivan is on a tour of Central Europe and the Western Balkans to shore up support against what the State Department calls "Russia’s aggression on the region."

Slovak Defense Minister Peter Gajdos signed the contract on December 13 with Lockheed Martin's vice president of international business development, Ana Wugofski.

"I'm delighted to be here today to witness this historic, very important moment," Sullivan said. "This is a significant step for Slovakia in it is own defense, as an important NATO ally, and as an important step forward in the bilateral relationship between the United States and Slovakia."

The first four jets are scheduled to be delivered by 2022, and the remainder a year later. The F-16 Block 70/72 fighter jets will replace the Slovak Air Force's Soviet-made MiG-29 jets.

Slovak Prime Minister Peter Pellegrini said his country will pay over 1.6 billion euros ($1.8 billion) for the warplanes. The deal also includes ammunition and the training of pilots.

Sullivan is also scheduled to visit Vienna, Sofia, Sarajevo, Skopje, and Warsaw on the trip, which will run through December 20.

In Vienna, Sullivan is expected to thank Austria for its contributions to security cooperation in Afghanistan and the Western Balkans “and will emphasize to senior officials the need to counter Iranian and Russian malign activities,” the statement said.

It added, though, that “notwithstanding continued concerns with Russia’s destabilizing activity,” Sullivan will in Vienna lead a “counterterrorism dialogue with Russian Deputy Foreign Minister Oleg Syromolotov, aimed at exploring areas “in which cooperation could benefit the security of the American people and prevent future terrorist attacks.”

On December 16, in Sarajevo, Sullivan will press officials to work to “maintain stability and continue reforms and a path to the West.”

The State Department said Sullivan’s stop in Skopje on December 18 will represent the highest-level U.S. diplomatic visit to Macedonia since 2001.

He will discuss regional issues, including efforts to implement the 2018 Prespa Agreement, under which Macedonia agreed to rename itself North Macedonia in exchange for Athens' promise to stop blocking its entry into NATO and the EU.

Greece has long maintained Macedonia's current name implies a claim on its own northern province of the same name and to Greece's ancient cultural heritage.

In Warsaw on December 19, Sullivan will "reaffirm the United States’ ironclad commitment to the NATO alliance," the State Department said.