US Secretary of State Mike Pompeo called on Turkey not to make Russia’s S-400s ‘operational.

"There could be more sanctions to follow, but frankly, what we'd really like is the S-400 not to become operational," Pompeo said in an interview with Bloomberg. "That's our objective. It’s what we've been talking to the Turks about for months and months. We've told them that it's simply incompatible with the F-35.”

Earlier, President Donald Trump made it clear that he would prefer not to impose sanctions on Turkey for the S-400s. He reported this to Republican legislators in a private meeting on Tuesday. Last week, the White House announced that it would no longer allow Turkey to participate in the F-35 program because of the purchase of a Russian missile defense system.

The Secretary-General’s comments on the S-400 also echo the statements made by Senator Lindsay Graham, who told the Defense Department the day before that he had talked with Turkish Foreign Minister Mevlüt Cavusoglu the day before at the request of the President.

On Twitter, Senator Lindsey Graham said the U.S. and Turkey "must find a way to avoid the damage to the relationship that comes from Turkey activating" the S-400 missile system.

Lawmakers said Trump should act in accordance with the Law on Counteracting US Enemies through the 2017 sanctions, and analysts pointed out that the president has no place to make an exception for Turkey.