(Reuters) – U.S. President Donald Trump said in a tweet that North Korea’s leader Kim Jong Un had insulted him by calling him “old” and said he would never call Kim “short and fat.”

Trump made the comment Sunday morning after attending the Asia-Pacific Economic Cooperation (APEC) summit in Vietnam.

In a series of tweets he also said Chinese President Xi Jinping was “upping sanctions” on North Korea in response to its nuclear and missile programs and that Xi wants Pyongyang to “denuclearize.”

Trump tweeted: “Why would Kim Jong-un insult me by calling me ‘old,’ when I would NEVER call him ‘short and fat?’ Oh well, I try so hard to be his friend – and maybe someday that will happen!”

Trump has traded insults and threats with Kim in the past amid escalating tensions over Pyongyang’s nuclear and missile programs.