"It is no secret that this president has little diplomatic knowledge or experience nor does he have the patience to devote the time necessary to fully prepare for a high level summit," Panetta said. "Without a comprehensive and well thought out strategy working closely with our allies, this president is likely to walk into a summit believing that the strength of his personality alone plus his gut instincts will be enough to prevail. That is a recipe for disaster."

In a serious negotiation, Trump would have to press Kim to freeze nuclear and missile testing, stop the production of nuclear weapons fuel and the deployment of nuclear weapons, and establish a verification process involving an inspection regime, according to Panetta.

In return, the US and its allies would have to consider concessions such as a reduction in the US troop presence in South Korea, economic aid and a peace treaty with the North.

"The reality is that the president has two choices to avoid disaster," Panetta said. The first choice would be to "assume that the summit will largely be a photo op with Kim Jong-un, with an agreement on a broad framework of issues to be considered in future negotiations, and a decision on a place and time for an agreed set of negotiators to begin discussion on the specifics of a possible agreement."

The second choice would be to "postpone any summit until designated negotiators have determined that there is in fact a set of elements and conditions that can be agreed to that will result in the denuclearization of North Korea."

"The president indeed deserves some of the credit for bringing about this situation due to the increase in sanctions and his relationship with (Chinese) President Xi (Jinping)," Panetta noted. "But to be successful, it will take time, serious preparation, careful planning and extensive consultation with our allies. Tweeting will not do it!" (Yonhap)