A South Korean official on Tuesday warned that North Korea is increasing its nuclear capability more rapidly than previously estimated as it seeks to build a nuclear missile capable of reaching the mainland U.S.

"North Korea has been developing its nuclear weapons at a faster-than-expected pace,” said Cho Myoung-gyon, the unification minister for South Korea, as reported by the Yonhap News Agency.

“We cannot rule out the possibility that North Korea could announce its completion of a clear force within one year,” Cho said.

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Cho cited 2018, the 70th anniversary of the Korean peninsula's separation into two states, as a crucial year for Pyongyang's nuclear ambitions, which have proven to be a thorn in the side of President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE during his first year in office.

Pyongyang in September said it had successfully tested a miniaturized hydrogen bomb that can be placed on an intercontinental ballistic missile (ICBM), causing the United Nations Security Council to unanimously vote to ramp up sanctions.

The North’s aggression has caused increased concern in the region, particularly from its southern neighbor and Japan. Pyongyang fired a ballistic missile over Japan in August and again in September.

"It is a fact that we have witnessed some noteworthy movements in North Korea. But it remains to be seen whether Pyongyang would make further provocations," Cho said in the reported remarks.

His comments add to the ongoing threat from North Korea, which in July conducted two ICBM tests.

Trump, who recently returned from a 12-day tour of Asia where North Korea’s aggression was a key focal point, has cautioned Pyongyang against making provocations toward the U.S.

“Today, I hope I speak not only for our countries but for all civilized nations when I say to the North: Do not underestimate us, and do not try us. We will defend our common security, our shared prosperity and our sacred liberty,” Trump said during a speech earlier this month to South Korea’s National Assembly.