Former Montenegrin President Ranko Krivokapić on Wednesday hit back at President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE’s suggestion that defending Montenegro could get the U.S. drawn into a world war.

Krivokapić, who served as president of the country of fewer than 1 million from 2006-2016, told the BBC that Trump was the “strangest” American president ever.

"He's the strangest president in the history of the United States," Krivokapić said.

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In an interview with Fox News’s Tucker Carlson that aired late Tuesday, Trump questioned the U.S.’s obligations to NATO allies after Carlson asked why his son should “go to Montenegro to defend it from attack?"

“I’ve asked the same question," Trump said in response. "Montenegro is a tiny country with very strong people. ... They are very aggressive people, they may get aggressive, and congratulations, you are in World War III."

Article 5 of NATO, which has only been invoked once, after 9/11, calls for member nations to defend other members if they are attacked. Montenegro was admitted into NATO in June of last year.

Krivokapić questioned Trump’s knowledge of foreign policy following the comments.

"With this kind of president, with his knowledge of foreign policy, who knows what is going on?” he asked. “Foreign policy is not his big thing."

He also said that Trump does not have to worry about such a situation, saying: "Peace in Montenegro is not in any kind of danger. Everything is under control. NATO forces are not required in Montenegro."

Trump’s comment about Montenegro drew sharp backlash from Senate Armed Services Committee Chairman John McCain John Sidney McCainThe Memo: Trump's strengths complicate election picture Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' Cindy McCain: Trump allegedly calling war dead 'losers' was 'pretty much' last straw before Biden endorsement MORE (R-Ariz.), who said that Trump is “playing right into” the hands of Russian President Vladimir Putin.

Montenegrin and U.S. officials have said that a 2016 coup attempt in the country was sponsored by Russia as an effort to stop the country from joining the transatlantic alliance.

"By attacking Montenegro & questioning our obligations under NATO, the President is playing right into Putin’s hands,” McCain said. “Putin will do anything to shatter the transatlantic alliance.”