South Korea is keeping close tabs on North Korea's nuclear and missile activities, the unification ministry said Monday, following a news report that the secretive nation seems to be operating related facilities at its Yongbyon complex.

"With regard to North Korea's nuclear and missile activities, including Yongbyon, (we) have been closely tracking and monitoring (them) on the basis of close South Korea-US coordination," ministry spokesperson Lee Jong-joo said at a press briefing.

Olli Heinonen, former deputy director-general at the International Atomic Energy Agency, told the Voice of America (VOA) earlier that there are indications of the North having activated its plutonium and uranium enrichment facilities in Yongbyon, with snow on the roof of some of the facilities shown melting. (Yonhap)