US President Donald Trump says he told the top US 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," Mr Trump wrote on Twitter, using his sarcastic nickname for Mr Kim.
Mr Trump's comment came the day after Mr Tillerson disclosed the US 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!" Mr Trump said.
- 'My daughter would be better than Trump' - Kim Kardashian
- Trump fires back at Kim in war of nuclear words
Mr Tillerson said during a trip to China on Saturday the US was probing North Korea to see whether it is interested in dialogue and that it had multiple direct channels of communication with Pyongyang.
This was the first time the Trump administration acknowledged it was in direct communication with Pyongyang.
The disclosure came as Mr Tillerson expressed hope for reducing tensions with North Korea, which is fast advancing towards its goal of developing a nuclear-tipped missile capable of hitting the US mainland.
"We are probing, so stay tuned," Mr Tillerson told a small group of reporters during a trip to China. "We ask: 'Would you like to talk?'" He said the US had "a couple of, three channels open to Pyongyang".
Mr Trump has vacillated between direct personal attacks on the North Korean leader and a willingness to negotiate. After announcing new US sanctions last month on North Korea, he also acknowledged diplomacy was still possible, asking: "Why not?"