ISTANBUL (Reuters) - U.S. President Donald Trump has the authority to waive sanctions on Turkey for its purchase of Russian air defense systems and should find a “middle ground” in the dispute, President Tayyip Erdogan said on Sunday.

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Erdogan’s comments came two days after NATO member Turkey took delivery of the first consignment of advanced Russian S-400 missile defense system parts, despite warnings from Washington that the move would trigger U.S. sanctions.

Broadcaster Haberturk quoted Erdogan as telling Turkish journalists that Trump “has the authority to waive or postpone CAATSA”, referring to U.S. sanctions designed to prevent countries buying military equipment from Russia.

“Since this is the case, it is Trump who needs to find the middle ground,” Erdogan said, according to Haberturk.

Trump expressed sympathy for Turkey’s position when he met Erdogan at a G20 summit in Japan last month, saying Ankara had bought the S-400s from Moscow because the previous U.S. administration would not sell it the Patriot defense system made by Raytheon Co.

“Right now, I don’t believe Trump is of the same opinion of those below him and he has said this in front of all the world’s media,” Erdogan said. “By buying the S-400s, we are not getting ready for war. We are trying to guarantee peace and our national security.”

Despite Trump’s warm words, U.S officials said last week the administration still planned to act.

U.S. Secretary of State Mike Pompeo told the Washington Post in an interview published late on Sunday “the law requires that there be sanctions and I’m confident that we will comply with the law and President Trump will comply with the law”.

U.S. officials have said Turkey could also be thrown off the F-35 stealth fighter jet program in addition to the threatened CAATSA sanctions, meaning it would no longer be part of the production process or be able to buy the jets it has ordered.

The Pentagon says the S-400s would pose a threat to the jets if they were operating in the same region. Erdogan said Turkey had orders for more than 100 F-35s made by Lockheed Martin and expected Washington to remain committed to the deal.

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

“Trump has always viewed this positively,” he said. ” ... Now, at a time when we are discussing mutual trade volumes of $75 billion, $100 billion, will we be dealing with this gossip? Why should we? We are strategic partners, let’s do what strategic partnership entails.”