SEOUL, Dec. 13 (Kyodo) — South Korea's main spy agency has said North Korea is fully prepared to conduct its third nuclear test at any time in the wake its successful launch of a long-range rocket Wednesday, Yonhap News Agency reported Thursday.

The report, which cited ruling Saenuri Party lawmaker Chung Moon Hun, said Won Sei Hun, head of the National Intelligence Service, told a parliamentary intelligence committee meeting Wednesday that the North is prepared to test-blast a nuclear device at any time, "even today or tomorrow if it wants to."

A nuclear test following a long-range missile test fits the pattern of North Korean behavior.

In 2006, Pyongyang carried out its first nuclear test three months after the test-firing of its long-range Taepodong-2 rocket. The second nuclear test in 2009 came just one month after a long-range rocket launch.

Yonhap said South Korea has strengthened surveillance over the North's underground nuclear test site at Punggye-ri in the northeastern province of North Hamgyong, where the two previous tests were conducted.

Earlier this year, it was reported that North Korea has built two new tunnels at Punggye-ri in a possible preparation for its third underground nuclear test.

Yonhap quoted South Korean officials as saying they cannot rule out the possibility of North Korea setting off a nuclear device built with highly enriched uranium this time, unlike two previous tests where plutonium was used.