Former U.S. Ambassador to the United Nations Bill Richardson lauded President Trump on Wednesday for improving diplomatic relations with Pyongyang, but warned administration officials to beware of North Korean leader Kim Jong Un's "end game."

"You want Kim Jong Un to talk to foreign leaders," Richardson told CNN after Kim met with Chinese President Xi Jinping in Beijing this week, his first foreign trip since ascending to power in 2011.

"He was only talking to Dennis Rodman before, so this is a good move. This is positive. This may lead to something decent," he added, referring to the former NBA star who has made multiple trips to North Korea in recent years and has called Kim "a friend for life."

But Richardson noted that Kim appeared to be "on the offensive" and shouldn't be underestimated.

He said he was also worried that Trump's tweets could derail a possible summit between Kim and the president, echoing concerns he expressed in November when Trump wrote that Kim was "short and fat" on Twitter.

"He's going to want to stay in office. He's not going to want to denuclearize completely I don't think," Richardson continued. "He's got a plan."

Richardson served as U.N. ambassador during the Clinton administration. He was also the governor of New Mexico from 2003 to 2011.