Turkish Foreign Minister Mevlüt Çavuşoğlu attends a news conference in Ankara, Turkey, on April 1, 2019. Reuters

Turkish Foreign Minister Mevlüt Çavuşoğlu doesn't know what the U.S. foreign policy is in Syria, he told CBS News' Margaret Brennan Wednesday. At an Atlantic Council event marking the 70th anniversary of NATO, she asked him directly, "Do you know what the U.S. foreign policy in Syria is?"

Çavuşoğlu replied, "No," a response that drew laughter from the audience. "And that is the problem," he added.

Brennan had been talking with him about the U.S. withdrawal from Syria, which Turkey welcomes, but it became apparent that Çavuşoğlu's sense of U.S. plans in Syria differ from the Trump administration's plans.

He mentioned that he thought 200 U.S. troops would be staying in southern Syria. Since the effective defeat of the Islamic caliphate, the Trump administration has said that the number of troops is higher — 400 troops. Two hundred would be peacekeeping troops, and the other 200 would be deployed in northeast Syria.

Çavuşoğlu said that Turkey has been receiving mixed messages. Different departments — including the State and Defense Departments, as well as CENTCOM — give "different positions, different statements."

"There is no clear strategy," Çavuşoğlu said. But he said that he would be discussing Syria with his counterparts in Washington over the next couple of days during the NATO conference of ministers.

Brennan, who is the moderator of "Face the Nation" and senior foreign affairs correspondent for CBS, raised another thorny issue with the Turkish foreign minister, too -- Turkey's plan to purchase of a Russian S-400 surface-to-air missile defense system, which the U.S. believes could endanger NATO planes. Asked if Turkey intended to proceed with the acquisition, Çavuşoğlu said "Definitely. It's a done deal."

He said that President Trump had "admitted" that "it was the mistake of the [Obama] administration" that the U.S. can't sell Patriot missiles to Turkey, and he argued that Turkey had no choice but to buy the Russian system. However, should that sale go through, the U.S. has threatened to sanction Turkey. Çavuşoğlu told Brennan that the agreement with Russia was finalized before the sanctions law was implemented, so "it shouldn't" apply.

But the Pentagon has already suspended delivery of the F-35 fighter jets as retaliation for buying the Russia defense system, stalling the sale of 100 jets to Turkey. But Çavuşoğlu said President Trump had told Turkey's President Recep Erdoğan in a 'recent' phone call that he would take care of the issue.

There has also been some concern that the S-400 is incompatible with NATO's own early-warning system, though Çavuşoğlu insisted that Turkey does not want or need to integrate it with that of the Alliance.

And anyway, Turkey shouldn't "have to choose between Russia" and other countries, Çavuşoğlu said, arguing that other NATO allies have economic ties to Russia, buying oil and gas from Russian companies. Like them, "we don't see our relationship with Russia as an alternative to others," he said.