UPDATE 1-Trump expecting 'positive' letter from N.Korea's Kim Jong Un soon

U.S. President Donald Trump on Friday said a letter from North Korean leader Kim Jong Un, which he believes will be positive, is on its way to him.

"I know that a letter is being delivered to me, a personal letter from Kim Jong Un to me. It was handed at the border ... yesterday," he told reporters on board Air Force One. "It's being delivered. It's actually an elegant way... and I think it's going to be a positive letter."

The two leaders have traded correspondence as they negotiate over North Korea's nuclear program, as well as messages over social media. On Thursday, Trump thanked Kim on Twitter for expressing "unwavering faith in President Trump."