U.S. President Donald Trump has said Turkey’s purchase of Russian S-400 missile defense systems creates "serious challenges" that he hopes can be resolved.
Trump made the comments on November 13 after holding what he called "wonderful and very productive" talks with Turkish President Recep Tayyip Erdogan at the White House, as relations between the two NATO allies are at one of their lowest points in decades.
Washington and Ankara hit a new crisis point last month over Syria, after Ankara launched a cross-border incursion to drive out a Kurdish militia, Washington's main partner in the fight against the Islamic State extremist group.
Trump had warned his Turkish counterpart in an undiplomatic letter to avoid too much bloodshed.
"Don't be a tough guy. Don't be a fool!" Trump said in the letter, which Erdogan reportedly threw in the trash.
In July, Turkey received its first S-400 shipment, prompting the United States to kick Ankara off its F-35 fighter jet program.
Washington says the sophisticated weaponry is incompatible with NATO equipment.
Turkey is "a great NATO ally and a strategic partner of the United States," Trump told a joint press conference with Erdogan, adding, "I'm a big fan of the president."
Erdogan insisted dialogue was needed to resolve the S-400 issue and that Turkey was prepared to buy U.S. Patriot missiles "if offered with the desired conditions."
He said, "We can overcome the tests we are facing, particularly regarding the S-400 system and F-35, only through dialogue."
Erdogan also said that Turkey was "hurt deeply" by last month's nonbinding House resolution describing the killings of Armenians in the Ottoman Empire at the beginning of the 20th century as genocide.
He said the move, which was a clear rebuke to Ankara in the wake of its invasion of northern Syria, had the potential to cast a "deep shadow over our bilateral relations."
Before flying to Washington, Erdogan acknowledged that he was making the visit "at a period when Turkish-American relations are going through a painful process."