North Korea said Thursday it will nullify all cross-border agreements on economic cooperation and liquidate South Korean assets in the country in response to Seoul's latest sanctions. 

"From this moment, we will view all agreements which the two Koreas have made on economic cooperation and exchanges as invalid," said a spokesman at the committee for handling inter-Korean affairs.

The North also said that it will sell off all assets by South Korean companies in North Korea, pointing to the South's decision to suspend an inter-Korean tour project at Mount Kumgang and to shut down a joint industrial park in the North.

The North's abrupt announcement came as South Korea on Tuesday unveiled a set of its own punitive sanctions against the North over Pyongyang's latest nuclear test and long-range rocket launch.

The measures included a ban on the entry of vessels that have made a port call in the North and blacklisting of key North Korean officials and entities.

Seoul's move came as the United Nations Security Council last week adopted a new resolution for tougher sanctions and South Korea took its toughest non-military action in February -- the shutdown of a jointly run industrial complex with the North.

On Feb. 10, South Korea closed the Kaesong Industrial Complex in the North's border city of Kaesong in response to the North's latest provocations.

The day after, North Korea expelled South Koreans staying at the factory zone and froze assets owned by South Korean firms. The North also designated the Kaesong complex a military-controlled area.

In 2008, North Korea froze and liquidated South Korean assets at Mount Kumgang after Seoul suspended the tour program there, following the shooting death of a South Korean tourist.

North Korea also threatened that it is ready to stage "pre-emptive" attacks against South Korea, vowing to deal a "deadly" blow to President Park Geun-hye.

The North has ratcheted up its belligerent rhetoric as its leader Kim Jong-un has said that his country has made nuclear warheads small enough to be mounted on ballistic missiles.

Earlier in the day, North Korea fired two short-range missiles into the East Sea in a show of protest against the ongoing annual joint military drills between Seoul and Washington. (Yonhap)