South Korea has stepped up surveillance in cyberspace to counter possible provocations by North Korea as tension runs high amid the communist country's threats of a nuclear war, the communications watchdog said Tuesday.

Following Pyongyang's nuclear test last month, Seoul has issued the fourth-highest level of cyber alert and has been conducting 24-hour monitoring of the state telecommunications network, according to the Korea Communications Commission.

South Korea's cyber alert system consists of a five-notch scale, with the third-highest level issued when an attack is detected.

The watchdog said a government team that includes the military has inspected its system and activated an international cooperation channel.

As part of efforts to combat North Korean threats, South Korean Prime Minister Chung Hong-won visited the state-run Korea Internet & Security Agency (KISA) last week to encourage heightened preparation against potential cyber attacks.

Meanwhile, the KCC urged Internet users to update antivirus programs on their computers and report any irregularities to KISA.

The moves come amid growing speculations that Pyongyang may launch unexpected provocations, including those in cyberspace, in response to a joint military drill by Seoul and Washington.

On Monday, South Korean and U.S. forces kicked off their annual Key Resolve military exercises despite Pyongyang's threat to nullify the cease-fire agreement that ended the 1950-53 Korean War and nonagression treaty signed with Seoul.

Continuing its threats to strike back against the two countries, the North's Committee for the Peaceful Reunification of Korea said in a statement "the U.S. and south Korean puppet forces are wholly to blame for all the ensuing catastrophic consequences from this moment." (Yonhap News)