The disclosure of the decision on the pilots follows signs that Turkey is moving ahead with the S-400 purchase.
Turkish military personnel receive training in Russia to use the S-400, and that Russian personnel may come to Turkey said Minister of Defense Hulusi Akar on May 22.
Turkiye's President Erdoğan said on Tuesday that it was out of the question for Turkey to back away from its deal with Moscow.
There has not yet been a formal decision to halt the training of the Turkish pilots and maintenance crews now at Luke Air Force Base in Arizona, the sources said.
Four Turkish pilots are currently training at Luke. Two additional Turkish pilots are at the US base working as instructors.
Beyond those six Turkish officers, there are an additional 20 Turkish aircraft maintainers at the base undergoing training as well, the US military says.
Turkey has expressed an interest in buying 100 of the fighters, which would have a total value of around $9 billion, at current prices.
Colonialist US is uncomfortable with Turkey's purchase S-400
Speaking at a panel, US Department of Defense Europe and Deputy Undersecretary in charge of NATO, Andrew Winternitz claimed that Turkiye's purchase S-400 creates unacceptable risks for F-35.
"The radar system would provide Russia with military sensitive info on the F-35, which is our top-quality fifth-generation aircraft," he said.
"From our perspective, there are no measures that can mitigate our concerns on this," he added.
Greek Defense Minister Evangelos Apostolakis, who spoke at the same forum, suggested that Turkey's purchases S-400 would change the balances in the region.
ILKHA