"Historians will remember such a policy is paving the path to war," said Cha, who is now a professor and senior adviser at the Center for Strategic and International Studies.

"The portfolio of pressure and diplomacy in the administration of the past 25 years has been ineffective," the professor said, highlighting progress North Korea has made in its nuclear weapons program in those years.

"The North Korean nuclear program is no longer a small program. ... The threat faced in the theater of North Korea's nuclear progress will enlarge to a (US) homeland security threat in the tenure of the current administration," he noted.

"In general we seek to minimize risks when we deal with North Korea, but this minimization has ... restricted options available to us and allowed the DPRK to incrementally but significantly grow their program," he said, implying that the Trump administration should be willing to take a higher risk of negotiating again with the regime.

The DPRK stands for the Democratic People's Republic of Korea, the North's official name.

Cha referred to the adoption of secondary sanctions on third countries doing business with North Korea, diplomatic pressure on North Korea's human rights record as tougher measures applicable to the new administration's approach to North Korea. He also called for greater roles by China and Russia to twist North Korea's arm.

"Russia has traditionally been a big player on the Korean Peninsula and the six-party talks. There may be an opportunity for a larger Russian role if there's a different relationship that the Trump administration has with Russia," according to Cha.

Still, questions remain over Washington's willingness to talk to the Kim Jong-un regime, he stressed.

Whether the new US administration is willing to open negotiations with regard to a peace treaty with North Korea or pay for a freeze on the regime's nuclear program, key issues must be answered first before entering into dialogue.

"For some reason, it's hard for me to imagine Donald Trump pay for a freeze," he said. "Without answers to these, you can't begin a negotiation, a negotiation that has potential to do more than what the previous ones have done." (Yonhap)