US President Donald Trump has refused to criticise Turkey’s acquisition of the Russian S-400 missile system, assailed by the Pentagon and NATO, making no mention of sanctions that Washington had threatened over the purchase.

“Turkey was forced into the move by his predecessor Barack Obama, and that he understood why they opted to buy the Russian missiles,” Trump said in his first comments since Turkey began the purchase of the S-400 system last week.

“I’ve had a good relationship with President Recep Tayyip Erdogan,” Trump further said.

“It’s a very tough situation that they’re in and it’s a very tough situation that we’ve been placed in… With all of that being said, we’re working through it — we’ll see what happens,” he added.

Donald Trump called it a “complex situation,” noting that the Pentagon has suspended Turkey from participating in the NATO F-35 fighter jet production program and from buying a planned 100 F-35s.

“Because they have a system of missiles that’s made in Russia, they’re now prohibited from buying over 100 planes. I would say that Lockheed isn’t exactly happy. That’s a lot of jobs,” Trump said while referring to the F-35 manufacturer Lockheed Martin.

Turkish President Recep Tayyip Erdogan had earlier said that “US President Donald Trump has the authority to waive sanctions on Turkey” for its purchase of Russian air defence systems and should find a “middle ground” in the dispute”.

The S-400 is known as Russia’s most advanced long-range surface-to-air missile defence system.

The S-400 missile defence system deal could result in US sanctions under the Countering America’s Adversaries Through Sanctions Act (CAATSA) instituted by the US Congress on arms purchases from Russia.

Erdogan said on Sunday, “Turkey still wanted to buy Patriot missile defence systems from Washington and the two countries should be aiming to increase trade and work on comprehensive defence cooperation”.

The supplies of the S-400 missiles to Turkey will begin in the first half of July, Erdogan had said earlier this month after returning from the summit of the Conference on Interaction and Confidence Building Measures in Asia held in Tajikistan’s Dushanbe.

President Erdogan hailed the controversial delivery of the S-400 Russian missile defense system despite the threat of US sanctions as Turkey marked the third anniversary of a bloody coup attempt on Monday.