US President Donald Trump said on Sunday that he told the top U.S. diplomat not to waste his time trying to negotiate with North Korean leader Kim Jong Un.

“I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man,” Trump wrote on Twitter, using his sarcastic nickname for Kim.

Trump’s comment came the day after Tillerson disclosed that the United States was directly communicating with North Korea on its nuclear and missile programs but that Pyongyang had shown no interest in dialogue.

“Save your energy Rex, we’ll do what has to be done!” Trump said.

Tillerson said during a trip to China on Saturday that the United States was probing North Korea to see whether it is interested in dialogue and that it had multiple direct channels of communication with Pyongyang.

Reuters