Trump says Tillerson is 'wasting his time' on talks with North Korea The president said the secretary of state should save his energy.

 -- President Donald Trump says he told Secretary of State Rex Tillerson that any negotiations with Kim Jong Un, whom Trump called “Little Rocket Man,” are a waste of time.

In an apparent response to news this weekend that the U.S. has open channels of communication with North Korea, the president also tweeted Sunday that Tillerson should save his energy because the U.S. will "do what has to be done."

Tillerson, speaking off-camera with reporters during his trip to China's capital, said Saturday that the administration is speaking to North Korea "directly, through our own channels."

"We have lines of communication to Pyongyang. We're not in a dark situation, a blackout," he said from the residence of the U.S. ambassador in Beijing. "We can talk to them. We do talk to them."

Tillerson said the Trump administration has "three channels" open with the regime of North Korean leader Kim Jong Un.

The top U.S. diplomat also said that broad sanctions against North Korea over its nuclear program "are beginning to have an effect."

"We are seeing from what we can observe, and the Chinese are telling us, that it is having some effect, and [the Chinese] have a pretty close view of it," Tillerson said. "But I also think it's the uniform voice coming from the international community. There is almost no one aligning with North Korea on this nuclear program of theirs."

This is not the first time Trump and his secretary of state have publicly differed in their statements on North Korea.

In June, Tillerson and Defense Secretary James Mattis said the U.S. and China were pushing ahead on applying diplomatic pressure North Korea. At the time, Trump tweeted that while he appreciated China’s efforts but they have “not worked out.”

On Saturday the secretary of state described the situation with Pyongyang as "overheated" after back-and-forth barbs between President Donald Trump and Kim Jong Un. Tillerson blamed North Korea for the rising tensions, saying that if it would stop testing missiles, that "would calm down things a lot."

Following Tillerson's remarks, U.S. Department of State spokesperson Heather Nauert issued a statement Saturday saying there are "several open channels" in which the Trump administration "can communicate" with the North Korean government, but officials in Pyongyang so far "have shown no indication that they are interested in or are ready for talks regarding denuclearization."

"U.S. diplomats have several open channels in which we can communicate with officials within the North Korean regime," Nauert said in the statement. "Despite assurances that the United States is not interested in promoting the collapse of the current regime, pursuing regime change, accelerating reunification of the peninsula or mobilizing forces north of the DMZ, North Korean officials have shown no indication that they are interested in or are ready for talks regarding denuclearization."