WASHINGTON -- A preventive military strike by the United States would not remove all of North Korea's nuclear and ballistic missile capabilities, a renowned American expert on the North Korean issue has said, while proposing economic sanctions as the most viable tool to end North Korea's nuclear weapons program.

"A preventive military strike would not destroy all of North Korea's capabilities. It would risk a wider war that would inflame South Korea and Japan and potentially cause millions of casualties," Michael Green, vice president for Asia at the Center for Strategic and International Studies, said last week in Washington, D.C. in his meeting with South Korean journalists.

Previously, he served as a senior director for Asian affairs at the National Security Council under former US President George W. Bush.

"It would also threaten the US because North Korea has an ability even without ballistic missiles to transfer nuclear weapons to terrorist groups, so a preventive military strike would not get all of North Korea's nuclear capabilities and would risk an unacceptable war," Green noted.

Diplomatic negotiations with Pyongyang would also not warrant resolution of North Korea's nuclear problem, given the country's track record of breaking previous agreements, he said.

"We shouldn't end sanctions or military exercises in order to have dialogue with Pyongyang because then we will prove there's no cost to North Korea for the path it's on," Green said, suggesting that the US build "infrastructure of sustained consequence" for North Korea to facilitate diplomacy work with the regime. "We now have to restore deterrence and restore credibility if we have any chance in medium to long run diplomacy."

Getting China to exert its influence in North Korea is crucial in the long run, he also highlighted.

"Chinese could be quite effective in significantly limiting North Korea's ability to obtain dual-use materials or technology for nuclear weapons program ... ability to transfer or proliferate those technologies outside of North Korea," according to Green.

"Chinese could be effective, if they sustain sanctions, at gradually changing the calculation of Pyongyang (though) it will take long time."

"Our strategy should be getting China to put pressure on North Korea. The best way to do that is to show a very tight US-Republic of Korea alliance," he said, adding that China does not want to see a stronger military alliance between Seoul and Washington or a war on the Korean Peninsula.

Such a calculation might have been behind President Donald Trump and Secretary of State Rex Tillerson implying possible military action against North Korea, he said. "China is the main target of this threat because the administration wants China to put pressure on North Korea." (Yonhap)