WASHINGTON, December 30. /TASS/. Washington keeps persuading Turkey not to buy air and missile defense systems from Russia, US Department of Defense Spokesperson Johnny Michael told TASS, commenting on the recent Turkish-Russian deal on S-400 systems.

"We have relayed our concerns to Turkish officials regarding the purchase of the S-400," the Pentagon spokesman said. "A NATO interoperable missile defense system remains the best option to defend Turkey from the full range of threats in its region."

"We have an open dialogue on this issue, and have emphasized the importance of maintaining NATO interoperability on any major defense systems procurements," the US official continued.

He said that Turkey and Russia have "robust and significant" defense-trade and military-sales relationship.

"Turkey continues to pursue anti-missile systems from NATO Allies, including the U.S. Patriot System, for its broader, long-term air defense needs. The United States is committed to expediting the delivery of equipment purchased by Turkey, when possible," the Pentagon spokesman said.

Earlier in the day, Russia and Turkey signed a loan agreement on Turkey’s purchase of Russian S-400 systems, Haberturk TV said on Friday. According to the Hurriyet daily, Ankara will pay part of the sum from its own funds and will contract a Russian loan for the rest. Notably, the loan will be in rubles.

On September 12, Turkish President Recep Tayyip Erdogan said Ankara had signed an agreement with Moscow on purchases of S-400 systems, with an advance payment already made. On November 2, Director General of Russia’s Rostec corporation Sergei Chemezov told TASS that the contract with Turkey on the sales of S-400 Triumf systems exceeded two billion US dollars. Supplies of these systems are expected to begin within two years.

Russia’s S-400 Triumf (NATO reporting name: SA-21 Growler) is the latest long-range antiaircraft missile system that went into service in 2007. It is designed to destroy aircraft, cruise and ballistic missiles, including medium-range missiles, and surface targets. The S-400 can engage targets at a distance of 400 kilometers and at an altitude of up to 30 kilometers.