It was the first time Trump has met with a South Korean official since taking office.

Further details were not immediately available.

Hong arrived in Washington earlier in the day on a mission to deliver Moon's letter to Trump and lay the groundwork for the first summit between the two leaders. His visit came after White House Asia Director Matt Pottinger visited Seoul earlier this week and the two countries agreed to hold a summit between Moon and Trump in Washington in late June.

Hong told reporters upon arrival that Moon asked to convey to the US government and the public his thoughts on the Korea-US alliance and the deployment of the US THAAD missile defense system.

THAAD is expected to be a key topic for Hong's discussions with US officials.

During the campaign, Moon was critical of the THAAD deployment decision, arguing that it was made without due process to collect public opinion. Presidential aides say the stance does not necessarily mean Moon is opposed to the deployment.

Trump fueled opposition to THAAD among the South Korean public by demanding the South pay for the $1 billion system. The demand runs counter to a deployment agreement in which the US agreed to pay for the system if the South agrees to host it and provide land.

Hong said he does not believe the two countries are at odds over THAAD.

Hong also said he will also outline Moon's stance on North Korea to US officials so as to dispel any misperceptions. (Yonhap)