The president must enact at least five of 12 possible sanctions, including denying USA visas to business executives or officials of that country, or denying access to American or other worldwide loans.

The Pentagon has twice pushed back a planned briefing today by senior officials on the subject, and it's unclear when anyone from the U.S. government will comment.

Turkey had attempted to purchase the S-400 in 2013 from China, but that deal fell through in 2015 due to North Atlantic Treaty Organisation disapproval.

Officials said that the White House stepped in and put a halt to DoD's carefully planned briefing, which had been scheduled for this morning.

"The delivery of parts belonging to the system will continue in the coming days", Turkey's Defence Industry Directorate said.

Turkey's Defense Ministry has posted photos of the first batch of the Russian-made S-400 missile system's equipment delivered to the country. "You have to treat people fairly". I don't think so.

Erdogan told Trump during their meeting on the margins of the G20 meeting in Japan that former U.S. President Barack Obama did not allow Ankara to buy Patriot missiles, an equivalent of the S-400s. "We have heard from him personally that this would not happen", Erdogan said.

Erdogan has said acquiring the Russian system is in line with Turkey's sovereign right to defend itself. "Everyone should know this".

US President Donald Trump's pick for Pentagon chief, Mark Esper, confronted the Turkish defence minister about the deal on the sidelines of a North Atlantic Treaty Organisation meeting last month.

Turkish media reports have said Turkey is expected to take delivery of two S-400 batteries. Washington has already halted training of Turkish pilots in the United States on the aircraft.

A North Atlantic Treaty Organisation official who spoke on the condition of anonymity was far less strident than the comments coming out of Washington.

"It is up to Allies to decide what military equipment they buy", a North Atlantic Treaty Organisation official tells NPR. The United States has threatened to impose sanctions on Ankara, saying Russian military hardware is not compatible with North Atlantic Treaty Organisation systems and that the acquisition may lead to Turkey's expulsion from an F-35 fighter jet programme.

Turkish Deputy Prime Minister Fikri Isik has defended the purchase, saying in 2017 as defense minister that Turkey needed a missile defense system and had negotiated with different nations.

Last month, Erdogan urged the United States to not let the purchase of the S-400 deteriorate strong ties between the two countries.

American Lawmakers from both sides of the aisle have opposed Turkey having both the S-400 system and F-35 jets.

"It did not have to come to this".

The alliance has repeatedly warned Turkey that the Russian system is incompatible with other North Atlantic Treaty Organisation weapons systems, not least the F-35, a new generation multi-role stealth fighter jet.

Plans are also under way to remove Turkey from the programme altogether.

Lockheed Martin is the primary airframe builder and Pratt & Whitney manufactures the propulsion system.The first F-35 Lightning II rolled out of the Lockheed factory in Fort Worth, Texas, in 2006.

Turkey, however, emphasised the S-400 would not be integrated into North Atlantic Treaty Organisation systems and would not pose a threat to the alliance.