On Monday, the United States said it was suspending Turkey's participation in the F-35 fighter-jet program due to Ankara's plans to buy Russia's S-400 missile defense system, raising fears that Moscow could gain data to hone its hardware and shoot down Western aircraft.
"Turkey's purchase of a $2.5 billion S-400 anti-aircraft missile system from Russian Federation poses great dangers to both that country and all of NATO", Pence said.
Turkish Foreign Minister Mevlut Cavusoglu appeared unmoved by the United States threats, saying the purchase of the S-400 system "is a done deal".
"We concluded the S-400 issue, signed a deal with the Russians and will start co-production", President Recep Tayyip Erdogan said last month.
The training for Turkish pilots in the US for the F-35 fighter jet project is continuing, said the official.
Vice President Fuat Oktay tweeted, in response to Mike Pence's demands.
In a PBS Newshour interview broadcast on Wednesday, Cavusoglu said Ankara proposed "to form a technical working group and to examine" any U.S. concerns over the S-400s.
The US has offered to sell Turkey the American-made Patriot missile defence system, but Mr Cavusoglu said it could not be delivered in time.
Turkey and Russian Federation have conducted three coordinated patrols in the mainly Kurdish-controlled northern Syrian region of Tel Rifaat and plan to continue the patrols, the sources said.
A small number of Turkish pilots are already training at Luke Air Force Base in Arizona on the next-generation aircraft and some of the plane's parts are manufactured in Turkey.
Other US officials have stopped short of threatening Turkey's underlying relationship with America or North Atlantic Treaty Organisation, but there have been growing calls for swift action, including sanctions, against Ankara to stop the S-400 purchase. In a letter to leading appropriators, House members called for fresh language last week restricting U.S. funding to support the jets if Turkey buys the S-400.
"Because Turkey is not just an F-35 purchaser, but an industrial partner, blocking delivery of these systems represents a major escalation by the United States as it threatens to impose serious costs on both sides", Hunter said. "Turkey is one of the partners of the F-35 program and fulfills its obligations in this regard", said the official.
The Trump administration has made great strides in recent months to transform the cash-strapped and perpetually ailing North Atlantic Treaty Organization into a viable global military force that has the capabilities to confront Russian Federation and other rogue regimes allied with terror forces.
Acting Defence Secretary Patrick Shanahan also expressed optimism, saying he was confident that the Patriot system proposal would work out.
He told reporters that the USA has made it clear to Turkey that the F-35 and the S-400 are incompatible systems, "but we're still working our way through that and hope we can come up with an arrangement".
Britons were nearly equal in the urge to protect as Americans, but opinion was an "even split" on whether to defend Turkey, while the French were more willing to defend the US and others apart from the Ukraine, Turkey, and Romania.