U.S. Sen. Lindsey Graham has reiterated his support for the Biden administration’s decision to sell F-16 fighter jets to Turkey, days after Washington’s strongest public backing yet for the request since it was lodged by Ankara last October.

U.S. President Joe Biden last week said that the United States should go ahead with the delayed sale of F-16 fighter jets to Turkey and that he is confident the congressional approval needed for the sale can be obtained.

Republican Senator of South Carolina Graham made a trip to Turkey over the weekend, where he met with Turkish presidential spokesperson Ibrahim Kalın.

The two officials discussed U.S.-Turkey bilateral relations, the fight against terrorism, cooperation in the defense industry, the Ukraine-Russia war, Black Sea grain shipments as well as other regional issues, according to a statement by the Turkish Presidency.

Cooperation in the field of defense and making progress on the F-16 issue will serve the interests of the two countries, the statement said.

In a tweet after the meeting, Graham said he had a “very productive trip” to Turkey, which, he stressed, is a “member of NATO and a valuable American ally.”

“While we have had a problematic relationship at times, it is imperative Turkey and the U.S. take steps to strengthen the ties between our two nations,” Graham wrote.

“I will do all in my power to support the Biden Administration’s decision to sell F-16s to the Turkish Air Force,” he said.

He added that the fighter jets will bolster the Turkish military that is “most definitely in America’s national security interests.”

Biden, as well as a senior Pentagon official, openly threw their support behind the potential sale and modernization of Turkey’s F-16 fleet, in a move that come after Ankara lifted a veto of NATO membership for Finland and Sweden.

President Recep Tayyip Erdoğan confirmed that Biden had told him during their meeting on the sidelines of the NATO summit in Madrid last week that he would do what he can regarding the Congress and the fighter jet deal.

Turkey last October made a request to the United States to buy 40 Lockheed Martin-made F-16 fighters and nearly 80 modernization kits for its existing warplanes, in what is estimated to be a $6 billion (TL 101 billion) deal.

Washington had not previously openly expressed any opinion on the sale aside from saying all weapons sales would have to go through the necessary legal process.

In March, the State Department wrote a letter to some members of the U.S. Congress who had opposed the sale, saying “appropriate” U.S. defense trade ties with Turkey would serve U.S. interests.

The sale of U.S. weapons to NATO ally Turkey became contentious after Ankara acquired Russian-made S-400 defense missile systems, triggering U.S. sanctions as well as Turkey’s removal from the F-35 fighter jet program.