A former U.S. presidential aide and Asia specialist says that neither normalization of U.S.-North Korea ties nor the signing of a peace treaty between the two countries is possible until Pyongyang fully denuclearizes.

Delivering a lecture Wednesday in Seoul, Georgetown University Professor Victor Cha went on to say that a nuclear North Korea was not acceptable to the U.S.-South Korea alliance.

Cha noted that Washington supports the upcoming inter-Korean summit talks, saying it hopes the summit will contribute to resolving the nuclear issue.

On the Seoul-Washington alliance, he said that, despite much noise in the past five years, the results have been good. He added that there was room for change concerning the scheduled transfer of wartime control of South Korean forces in 2012.