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President Barack Obama said Sunday that he doesn't take seriously North Korea's claim that it would halt nuclear tests if the U.S. suspends military exercises with South Korea.

North Korea's Foreign Minister Ri Su Yong made the ultimatum in an exclusive interview with The Associated Press Saturday hours after North Korea test-fired a ballistic missile from a submarine.

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"We don’t take seriously a promise to halt" nuclear tests, Obama said during a joint press conference in Hanover with German chancellor Angela Merkel.

He said the U.S. would engage in "serious conversations" with North Korea if the country shows that it is serious about ending its nuclear program.

"What is clear is that North Korea continues to engage in continuous provocative behavior, that they have been actively pursuing a nuclear program, an ability to launch nuclear weapons," Obama said. "And although more often than not they fail in many of these tests, they gain knowledge each time they engage in these tests."

U.S. President Barack Obama attends a press conference with German Chancellor Angela Merkel on April 24, 2016 in Hanover, Germany. Adam Berry / Getty Images

Obama is in Germany on two-day push to sell his trans-Atlantic trade pact, the Transatlantic Trade and Investment Partnership (TTIP). He said Sunday the U.S. and European Union need to "keep moving forward" on negotiations for a U.S.-Europe trade deal. He said Merkel agrees with him.

"What you’re seeing around the world is people are unsettled by globalization," Obama said. But "trade has brought enormous benefits," he said, adding that America has to stay competitive as regions in Asia and Africa begin to develop their economies.

Proponents argue that the deal would boost business at a time of global economic uncertainty. Critics fear the erosion of consumer protections and environmental standards.

While Obama repeatedly praised Merkel during their joint appearance and expressed appreciation over the U.S.-Germany relationship, he said he does not agree with her proposal to create "safe zones" to shelter refugees in war-torn Syria because of the military commitment that would be involved. "Who's going to put on a bunch of ground troops inside of Syria," Obama asked.

Still, he said the German chancellor was "on the right side of history" in her effort to aid the refugees in the midst of political push-back.

Merkel has received criticism at home for allowing thousand of people fleeing violence in Syria and other conflict zones to resettle in Germany. She recently helped Europe and Turkey negotiate a deal to help ease the migrant flow.