Defense Minister Song Young-moo describes a recent visit by senior North Korean official Kim Yong-chol to South Korea as an "unpleasant event" for the South Korean military.

Song spoke to lawmakers at the National Assembly Wednesday.

However, he refused to confirm directly whether Kim can be regarded as responsible for North Korea's attack on the South Korean Navy vessel Cheonan in 2010 which killed 46 sailors.

The minister did say he believes the submarine that carried out the attack belonged to the Reconnaissance General Bureau, widely is understood to have been under Kim Yong-chol's authority at the time.

Kim Yong-chol, who currently holds the title of vice chairman of the North Korean ruling party's Central Committee, returned home Tuesday after visiting the South for the PyeongChang Olympics closing ceremony.