WASHINGTON: US President Donald Trump told reporters at the White House on Monday his administration had very positive correspondence recently with North Korea, with which it has been working to restart talks aimed at ending Pyongyang's nuclear program.

"There was a little correspondence recently. Very positive correspondence with North Korea," Trump told reporters at the White House. He did not respond to questions about whether it was between and him and North Korean leader Kim Jong Un.

"When they're ready, we'll be ready," Trump said.

North Korea warned last week that if the United States broke a pledge not to hold military exercises with South Korea, it could put the nuclear talks at risk.

US Secretary of State Mike Pompeo has rejected the charge that military exercises would breach any agreement between Trump and Kim. And a top South Korean official said the US-South Korean military exercise would go ahead as planned next month.