South Korea has decided to raise its voice against North Korea's possession of biochemical weapons in international meetings following the Malaysian police's announcement that a VX nerve agent was used to kill Kim Jong-nam, the half brother of North Korean leader Kim Jong-un, foreign ministry officials said Saturday.

"The government will bring up the issue of North Korea's biochemical weapons programs when top nuclear envoys from South Korea, the United States and Japan meet in Washington on Monday, as well as during various multilateral talks based in Geneva and other locations," one of the officials said.

Kim Jong-nam, the eldest son of late former leader Kim Jong-il, died on Feb. 13 at an airport in Kuala Lumpur after apparently being poisoned by two Asian women. Malaysian police named eight North Koreans, including a diplomat, as suspects, though Pyongyang denies its involvement. 

On Friday, the police announced that Kim Jong-nam was killed with a VX nerve agent. VX is listed as a weapon of mass destruction by the United Nations and its use is banned under the Chemical Weapons Convention (CWC), to which North Korea is not a signatory.

"The government plans to take a tough stance on the killing of Kim Jong-nam," the other government official said. The third official said, "Things went out of control as the use of a chemical weapon was unveiled... The government is currently on the stage of trying to find the truth behind the case on the one hand and considering many different countermeasures on the other."

Seoul officials forecast that security threats from North Korea's biochemical weapons programs will likely be discussed during Monday's talks along with its main topic, the country's nuclear and missile programs.

Seoul will also call for relisting the North as state sponsor of terrorism during the meeting, officials said.

North Korea was put on the U.S. terrorism sponsor list for its 1987 midair bombing of a Korean Airlines flight that killed all 115 people aboard. But the U.S. administration of former President George W. Bush removed Pyongyang from the list in 2008 in exchange for progress in denuclearization talks.

The South Korean military believes North Korea has up to 5,000 tons of chemical weapons stockpiled, the third largest after the U.S. and Russia. (Yonhap)