SEOUL, June 23 (Yonhap) -- A key South Korean presidential aide on national security is visiting the United States for possible talks on inter-Korean relations and the ratification of a free trade agreement between Seoul and Washington, a source said Thursday.

Kim Tae-hyo, a senior secretary to President Lee Myung-bak for national security strategy, left for the U.S. on Wednesday, the source added, after an invitation from the White House.

"He is expected to meet key U.S. government officials and discuss pending issues on diplomacy and security," the source said on the condition of anonymity.

This is Kim's first trip to the U.S. since February. His current visit may also be related to a meeting between South Korean Foreign Minister Kim Sung-hwan and U.S. Secretary of State Hillary Clinton, scheduled for Friday in Washington, the source said.

Kim Tae-hyo is also expected to discuss future strategies on managing inter-Korean ties. The two Koreas' already frigid relations took a bizarre turn earlier this month, when Pyongyang claimed that Seoul proposed a series of summit meetings during their secret encounter in Beijing. Kim was cited by North Korea as one of the South Korean participants in that Beijing meeting.

Relations between the two Koreas have been tense since conservative President Lee took office in early 2008 with a policy linking aid to North Korea's commitment to denuclearization. The ties frayed further last year when North Korea torpedoed the warship Cheonan and shelled Yeonpyeong Island, killing a total of 50 South Koreans.

Seoul has demanded an apology as a precondition for resuming dialogue with Pyongyang, but North Korea has claimed innocence.