The US ambassador to the Philippines delivered the letter to Ri Yong Ho at a security forum in Singapore, according to the US State Department spokeswoman Heather Nauert.
Heather Nauert added that the letter was a response to one from Kim Jong Un to Donald Trump.
READ MORE: Kim Jong-un: 'Extraordinary Efforts' Made by Trump for Improving US-N Korea Ties
Earlier this year, the North Korean leader stated he was ready for denuclearization of the DPRK and signed a corresponding agreement with South Korean President Moon Jae-in at the inter-Korean summit in the truce village of Panmunjom in April.
In his earlier statement, Trump did not exclude the lifting of sanctions if the DPRK refused to use nuclear weapons, but the official policy of the United States is that sanctions will only be halted after "full, verifiable and irreversible" denuclearization.
