President Donald Trump has pushed Turkish President Tayyip Erdogan to walk away from buying a Russian missile defence system, describing it as a "very serious challenge," but he says he hopes the NATO allies will resolve the dispute.
After a much anticipated meeting at the White House to address a crisis in relations, Trump said he was "a great fan" of the Turkish leader and that they had a "wonderful and productive" encounter.
But both leaders fell short of explaining in concrete terms how they would overcome the mounting differences they have on numerous issues such as Syria policy and Turkey's purchase of the Russian S-400 missile defence system.
"Turkey's acquisition of sophisticated Russian military equipment, such as the S-400, creates some very serious challenges for us and we are talking about it constantly," Trump told a joint news conference.
"We talked about it today, we're talking about it in the future, hopefully we'll be able to resolve that situation."
Minutes after their news conference, the White House released a statement using firmer language. "In order to achieve progress on other fronts, it is vital that we resolve the issues involving Turkey's purchase of the Russian S-400 air defence system, strengthening our defence partnership," it said.
Turkey and the United States have been at loggerheads over the purchase of the S-400 system, which the United States says is not compatible with NATO defences and poses a threat to Lockheed Martin's F-35 'stealth' fighter jet.
Turkey had shrugged off threats of US sanctions and began receiving its first S-400 deliveries in July. To punish Turkey for its purchase, the United States has banned sales of F-35s to Turkey and removed the country from a multinational program to produce the warplane.
"We've asked our secretary of state and minister of foreign affairs and our respective national security advisers to immediately work on resolving the S-400 issue," Trump said.
Erdogan said that the two countries could only overcome their dispute on the S-400s and F-35s through dialogue. "We have agreed to open a new page in our relationship," he said.
Trump brought in five Republican senators to the White House to speak with Erdogan about the Syrian Kurds and the delivery of S-400s.
The two countries, which boast the two largest armies in NATO, hit a crisis point last month when Erdogan began his cross-border incursion against America's Kurdish allies in Syria and upended the US presence there.
In the news conference, Erdogan was critical of the US Congress, particularly of a House of Representatives vote last month in favour of a non-binding resolution recognising the killings of 1.5 million Armenians a century ago as a genocide, a symbolic but historic vote denounced by Turkey.