South Korea is put on high alert Monday following reports that Kim Jong Il, the top leader of the Democratic People's Republic of Korea (DPRK), died at the age of 69 of a heart attack.

Immediately after the DPRK's KCNA news agency reported that Kim died Saturday on a train, South Korean President Lee Myung-bak convened the National Security Council (NSC) to discuss follow-up measures with Cabinet ministers 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 and put them on standby.

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

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

Lee spoke separately with U.S. President Barak Obama and Japanese Prime Minister Yoshihiko Noda on the phone and agreed to closely cooperate with each other on the matter, his office Cheong Wa Dae said.

"Undivided public opinion is more important than anything else, " Lee said after a separate Cabinet meeting, according to Cheong Wa Dae. "Peace and stability on the Korean peninsula should not be threatened by the current situation," he said.

South Korea's military was also quick to respond to the news.

The Joint Chiefs of Staff (JCS) put military on emergency alert shortly after the news hit the press and called an emergency meeting.

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

South Korea's JCS chief Jung Seung-jo and James D. Thurman, commander of the U.S. Forces Korea, agreed not to raise the level of the Watchcon surveillance status, according to Yonhap.

"Since North Korea is in a lot of shock after passed away of its leader. The generals decided South Korea and the United States shouldn't create an unnecessary sense of crisis," Yonhap quoted a military official as saying.

Military authorities had been reportedly considering raising both the Watchcon and the Defcon defense readiness status.

South Korean police also intensified vigilance and tightened security at local airports and the U.S. embassy in Seoul. Major political parties here held emergency meetings, with the ruling Grand National Party calling for "bipartisan unity in the interest of national security."

The main opposition Democratic Party expressed condolences for Kim's "sudden death," and pledged bipartisan efforts for peace on the Korean peninsula.

Parliamentary speaker Park Hee-tae called emergency meetings of committees on foreign affairs, trade and unification, national defense and intelligence.

The South Korean government will temporarily suspend planned visits to the DPRK, except for South Koreans working at the joint industrial complex in the DPRK border town of Kaesong, the unification ministry in Seoul said.

The government has not yet to decide whether to officially express condolences or send a delegation to pay a condolence call, the ministry, which oversees inter-Korean relations, said in a press briefing.