South Korea's National Intelligence Service (NIS) said the Democratic People's Republic of Korea (DPRK) might conduct additional nuclear and long-range missile tests, Seoul's Yonhap news agency reported Tuesday.

The DPRK might opt for further provocation to influence the UN Security Council as the 15-member body meets to discuss joint responses to Tuesday's nuclear test conducted in defiance of UN resolutions, the NIS reportedly told a parliamentary intelligence committee.

The remark came after Pyongyang carried out its third nuclear test earlier today. An artificial earthquake with a magnitude of 4.9 was detected from the town, where the DPRK's nuclear test facility is located.

While the DPRK said it used a lighter, smaller nuclear device for the underground test, the spy agency voiced doubt over the claim, according to Yonhap.

Both South Korean President Lee Myung-bak and his successor Park Geun-hye strongly condemned the widely anticipated test, which they said violated UN resolutions and posed a threat to regional peace and stability.

South Korea's military was immediately put on heightened alert to deter potential cross-border provocations, while the South Korean and US forces upgraded their border surveillance level.

The defense ministry here is keeping an eye on developments in the DPRK to monitor potential signs of additional nuclear or missile tests. No unusual movements have been detected thus far.

Pyongyang recently vowed to proceed with missile and nuclear tests targeting the United States, its "sworn enemy," to protest the UN condemnation over its Dec. 12 rocket launch.

Pyongyang conducted nuclear tests in 2006 and 2009.