President Trump on Sunday rejected the idea of negotiating with the North Korean regime, in the process seeming to undermine his own secretary of State, Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE, who earlier in the weekend said Washington was in direct talks with Pyongyang.

“I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man,” Trump tweeted on Sunday morning, using his preferred nickname for North Korean leader Kim Jong Un.

“…Save your energy Rex, we’ll do what has to be done!” he added.

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The president’s tweets came a day after Tillerson said Washington had established direct lines of communication with North Korea.

“We ask, ‘Would you like to talk?’ We have lines of communications to Pyongyang — we’re not in a dark situation, a blackout. We have a couple, three channels open to Pyongyang,” Tillerson said on Saturday, according to The New York Times.

The secretary of State’s remarks, made during a visit to Beijing, were the first time the Trump administration had publicly acknowledged that it had established backchannel talks with Kim’s regime.

On Sunday, following Trump’s tweets saying Tillerson was “wasting his time” talking to Pyongyang, the State Department issued a statement on Twitter.

“[North Korea] will not obtain a nuclear capability. Whether through diplomacy or force is up to the regime,” spokeswoman Heather Nauert tweeted.

“Diplomatic channels are open for [Kim Jong Un] for now. They won’t be open forever,” she added.

But the president was quick to double down later Sunday.

“Being nice to Rocket Man hasn’t worked in 25 years, why would it work now? Clinton failed, Bush failed, and Obama failed. I won’t fail,” Trump tweeted on Sunday afternoon.

The conflicting messages from the White House and State Department come amid growing tensions on the Korean Peninsula, as Pyongyang continues to carry out missile tests in the region.

Last weekend, Trump provoked an angry response from Pyongyang after he warned that the country “won’t be around much longer” if it continues its threats against the U.S.

"In light of the declaration of war by Trump, all options will be on the operating table of the Supreme leadership of DPRK," the country’s foreign minister, Ri Yong Ho, said in New York, using the acronym for the Democratic’s People Republic of Korea, the country’s formal name.