SEOUL - South Korea is put on high alert Monday following the death of Kim Jong-il, the top leader of the Democratic People's Republic of Korea (DPRK).

Immediately after the DPRK's KCNA news agency reported Kim's death, South Korean President Lee Myung-bak convened the National Security Council (NSC) to discuss follow-up measures with officials including the foreign minister and the defense chief.

Lee also ordered all government employees be on emergency alert, a measure that would restrict their unauthorized leaves.

"The government will keep a close eye on developments in North Korea (DPRK)," Ahn Kwang-chan, a senior presidential secretary for national crisis management, said after the NSC meeting. "President Lee asked South Koreans to remain calm and focus on daily economic activity."

The president confirmed at the meeting all necessary measures are being taken based on the crisis management manual, Ahn added.

Lee also spoke with US President Barak Obama on the phone and agreed to closely cooperate with each other on the matter, his office Cheong Wa Dae said.

South Korea's Joint Chiefs of Staff (JCS), meanwhile, put the military on emergency alert and called an emergency meeting.

The JCS has stepped up border surveillance, but no unusual activity has been detected yet, according to the Seoul-based Yonhap News Agency.

JCS officials are reportedly considering raising both the Defcon defense readiness status and the Watchcon surveillance status.

South Korean police also intensified vigilance.