Washington (CNN) Secretary of State Mike Pompeo said that President Donald Trump is unlikely to keep the US in the Iran nuclear deal past the next deadline to certify the deal in May.

"The President has been clear -- absent a substantial fix, absent overcoming the shortcomings, the flaws of the deal -- he is unlikely to stay in that deal past this May," Pompeo told reporters during a press conference at NATO headquarters in Brussels.

Pompeo, on his first trip as the top US diplomat, also said the US and NATO were prepared to push back hard against Russia and congratulated South Korea and North Korea on their historic agreement to set aside their conflict and cooperate on denuclearizing their shared peninsula.

Until that happens, though, Pompeo warned that the "maximum pressure campaign" to exert financial and diplomatic pressure on North Korea will continue. Pompeo, who met secretly with North Korean leader Kim Jong Un, said he got the sense that Kim was serious about negotiations.

"I don't want to say anything about the meeting itself," Pompeo said, before adding that, "yes, I did get a sense that he was serious."

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