Victor Cha, a senior vice president and Korea chair at the U.S.-based Center for Strategic and International Studies / Yonhap

North Korea's nuclear missile program appears to be "unstoppable," with its progress apparently moving faster than U.S. modernization of its missile defense systems, a U.S. expert said Wednesday.

Victor Cha, a senior vice president and Korea chair at the U.S.-based Center for Strategic and International Studies, made the assessment during a forum here, while citing the nuclear-armed North's recent pushing for advancing its strategic weapons capabilities, including various types of missiles.

"I think we're currently in a situation where North Korea's nuclear missile programs really look like they're unstoppable right now," the former White House official said. Cha, who served as the director for Asian affairs at the National Security Council from 2004 to 2007, joined the forum via video links.

"The United States is expanding and modernizing their missiles and augmenting and supplementing their missile defense system," Cha added. "But I would argue that North Korea's progress on their programs is moving faster than our modernization of our missile defense systems."

Still, he stressed the need for continued diplomatic efforts, saying military actions can't be an answer.

He described the current situation as "not a good one for certain," noting Pyongyang's refusal to respond to dialogue offers from the Joe Biden administration.

Pyongyang has carried out a string of missile launches since the start of this year amid reports that it has even completed preparations for what would be its seventh known nuclear test. (Yonhap)