US President Donald Trump vowed Monday to "take care of" North Korea's nuclear and ballistic missile threats as he unveiled his administration's first national security strategy.

Trump said that he has pushed a campaign of "maximum pressure" on North Korea to produce the "toughest-ever sanctions" against the regime but more work remains to be done.

Tensions have flared up after North Korea lobbed a new intercontinental ballistic missile in late November, declaring that it has completed its nuclear armament.

US Secretary of State Rex Tillerson said last week that the US is ready to begin talks with North Korea "without preconditions" in a possible shift of US policy. But days later, he said that the North should halt its "threatening behavior" before talks can begin, backpedaling on his previous remarks.

Cho said that Tillerson's comment is nothing new, given that Washington has sounded out for talks with the North despite tragic events including the death of Otto Warmbier, an American college student who died in June after returning home in a coma following a monthslong detention in the North.

The envoy expressed hope that next year the atmosphere will be shifted to dialogue with Pyongyang.

"In my personal opinion, as the US has said it is open to dialogue with North Korea, it is time for the North to reply," Cho said.

"It is hard to predict how Pyongyang would react, but as North Korea has announced that it has completed its state nuclear force, I hope that in the new year, (the US and North Korea) would enter the phase for dialogue." (Yonhap)