Russian S-400 missile battalions participate in tactical training to counter attacks of potential sabotage and reconnaissance groups. Vitaly Nevar | TASS via Getty ImagesWASHINGTON – The Biden administration was unable to work out a resolution with Turkey following Ankara’s defiant purchase of a Russian weapons system, which the NATO alliance views as a security risk. National security advisor Jake Sullivan told reporters Thursday on a call that President Joe Biden and Turkish President Recep Tayyip Erdogan discussed the 2017 multibillion-dollar weapons deal with Russia this week at NATO’s headquarters.In December, the Trump administration slapped sanctions on Turkey, a NATO member, for buying the S-400 missile system in a confrontation not typically seen within the alliance.”On the S-400, they discussed it. There was not a resolution of the issue. There was a commitment to continue the dialogue on the S-400,” Sullivan said, adding that the Biden administration would have more to say on the matter after Washington and Ankara hold additional talks.Turkish President Recep Tayyip Erdogan (L) and US President Joe Biden (R) hold a meeting at the NATO summit at the North Atlantic Treaty Organization (NATO) headquarters in Brussels, on June 14, 2021.Murat Cetinmuhurdar | Anadolu Agency | Getty ImagesDuring a NATO press conference, Erdogan said he had not changed his position on the S-400 despite having a “sincere” meeting with President Joe Biden.Biden also said the meeting with Erdogan was productive, adding that he was confident the U.S. will “make real progress with Turkey.”Erdogan said on Tuesday that he told Biden to “not expect Turkey to take a different step on the F-35 and S-400 issues,” according to a report from Turkey’s state media.”We must monitor developments closely. We will be following up on all our rights,” he said. “In the next period, our foreign ministers, defense ministers and defense industry chairs will be moving this process forward by meeting with their counterparts,” Erdogan added.In multiple efforts to deter Turkey from buying Russia’s S-400 missile system, the State Department offered in 2013 and 2017 to sell the country Raytheon’s Patriot missile system. Ankara passed on the Patriot both times because the U.S. declined to provide a transfer of the system’s sensitive missile technology.A F-35 fighter jet is seen as Turkey takes delivery of its first F-35 fighter jet with a ceremony at the Lockheed Martin in Forth Worth, Texas, United States on June 21, 2018.Atilgan Ozdil | Anadolu Agency | Getty ImagesUnder the Countering America’s Adversaries Through Sanctions Act, or CAATSA, any foreign government working with the Russian defense sector finds itself in the crosshairs of U.S. economic sanctions.Despite warnings from the United States and other NATO allies, Turkey accepted the first of four S-400 missile batteries from the Kremlin in July 2019.A week later, the United States cut Turkey, a financial and manufacturing partner, from the F-35 program.Due to Turkey’s removal from the F-35 program, U.S. defense giant Lockheed Martin offered the jets originally slated to join Ankara’s arsenal to other customers.