Washington: President Donald Trump said on Thursday that Chinese President Xi Jinping "could be influencing" North Korean leader Kim Jong-un after his regime abruptly shifted to a sharp, negative tone this week about the prospects of a planned summit with the US in June.

"If you remember two weeks ago, all of a sudden out of nowhere Kim Jong-un went to China to say hello again -- second time -- to President Xi," Trump told reporters during an Oval Office meeting with NATO Secretary General Jens Stoltenberg, referring to a May 8 meeting between the leaders.

"It could very well be that he's influencing Kim Jong-un. We'll see what happens. Meaning the President of China, President Xi, could be influencing," Trump said.

North Korea suspended talks with Seoul earlier this week, citing long-planned US-South Korea military exercises. That decision came with a warning to the US to "think twice" about the fate of the Trump-Kim summit in Singapore on June 12.