A preemptive US military strike wouldn’t destroy all of North Korea’s nuclear and ballistic missile capabilities, according to a respected US expert who argues instead, that economic sanctions are the most viable way to end Pyongyang’s nuke weapons program.

Michael Green, the vice president for Asia at the Washington, D.C.-based Center for Strategic and International Studies (CSIS), reportedly told a meeting of South Korean journalists last week that such an attack would also trigger a larger conflict that could result in the deaths of millions, according to a report by South Korea’s Yonhap news agency.

“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,” Green was quoted as saying.

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

The expert also warned that North Korea’s threat to the US extended beyond one posed by nuclear-tipped missiles.

“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.

Green, at the same time, warned that diplomatic talks with Pyongyang alone won’t result in a resolution of the North’s nuclear problem, given the country’s track record of breaking previous agreements.

“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 an “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.”