Washington's top negotiator for its defense cost-sharing talks with Seoul is making an official visit to South Korea for four days.

James DeHart of the State Department is expected to arrive in Seoul on Tuesday afternoon. 

During his stay, he will attend an unofficial dinner with his South Korean counterpart Jeong Eun-bo and also meet with members of parliament and journalists as well as U.S. Forces Korea officials.

DeHart and Jeong last met in Hawaii in late October for the second round of defense cost talks. The third meeting will be held this month in Korea but a detailed timetable has yet to be determined.

It is unusual for a U.S. negotiator to make an unofficial visit to a country engaged in negotiations with Washington. 

A Foreign Ministry official in Seoul said that DeHart may be wanting to gauge public sentiment in Korea and expressed hope that it can be an opportunity for him to grasp the mood and listen to views on Seoul's request for a reasonable and fair cost-sharing deal. 

His visit is believed to be aimed at assessing Korea's stance on the cost issue in a bid to speed up negotiations. 

The current cost sharing deal expires this year. 

Technically, talks must conclude within the year for a new agreement to take effect in 2020. 

Washington wants Seoul to significantly increase its share of the cost for maintaining American troops in South Korea.