SIMI VALLEY, Calif. — Former Defense Secretaries Leon Panetta and James Mattis linked the failed summits between North Korean leader Kim Jong Un and President Donald Trump to a lack of preparation and not working with allies.

"If the president of the United States is going to sit down with another leader, you better damn well be prepared in terms of what are the issues involved and what do we have to agree on so that you get something accomplished," Panetta said when asked about Trump's meetings with Kim.

"Yes, we made some progress in trying to restrain what happens in North Korea but I think North Korea today represents every bit as great a threat as it did before, if not more," he added.

North Korea, the only nation to have tested nuclear weapons this century, spent most of Trump's first year in office perfecting its nuclear arsenal. Since 2011, Kim has fired more than 90 missiles and had four nuclear weapons tests, which is more than what his father, Kim Jong Il, and grandfather, Kim Il Sung, launched over a period of 27 years.

"We did not perhaps have the alignment of the department and we did not engage with our allies at a time where they had to read something in a newspaper about what was going on," Mattis said alongside Panetta at the annual Reagan National Defense Forum.