CNN reports that U.S. President Donald Trump has sent a letter to North Korean leader Kim Jong-un.

A source told the U.S. cable news channel that the letter was flown to Pyongyang and delivered by hand over the weekend.

The letter comes as Washington and Pyongyang negotiate details of a second summit between their two leaders.

The source also said Kim Yong-chol, North Korea’s former spy chief and one of the country’s top negotiators, could visit Washington as soon as this week to iron out the final details of the upcoming meeting.

CNN reported earlier that U.S. teams had scouted Bangkok, Hanoi and Hawaii as possible venues for the summit.