U.S. President Donald Trump said on Friday a letter from North Korean leader Kim Jong Un, which he believes will be positive, is on its way to him, a day after expressing fresh optimism about a denuclearization deal.

“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,” Trump told reporters on 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 and Trump has also praised Kim on social media. On Thursday, Trump thanked Kim on Twitter for expressing “unwavering faith in President Trump” and added: “We will get it done together!”

According to the South Korean officials, Kim said his faith in Trump was “unchanged” and he wanted denuclearization of the Korean peninsula and an end to hostile relations with the United States before Trump’s first term ends in early 2021.

However, there has been no indication that Kim has offered more concrete steps toward giving up his nuclear weapons and some U.S. officials privately doubt he is willing to abandon the arsenal.

Both Kim and Trump have stressed their personal relationship since meeting in an unprecedented June 12 summit which skeptics say was big on fanfare but short on substance.