"After completing an analysis and assessment of the North's missile tests, the government will likely come out with a much tougher countermeasure with regards to such issues as suspending the North's membership in the UN," a government official said on the condition of anonymity.

South Korea has been ramping up its push to suspend the North's memberships at global bodies including the UN, especially after the recent murder of Kim Jong-nam, the estranged half brother of the North's leader Kim Jong-un at an airport in Malaysia on Feb. 13.

The North is currently suspected of having been behind the murder, with eight of its people having been named as suspects.

Local authorities determined that Kim was killed by VX nerve agent, a prohibited chemical weapon.

In his speech at the Conference of Disarmament in Geneva late last month, Foreign Minister Yun Byung-se called for tough measures against the North violating human rights of its people and defiantly seeking missile and nuclear ambitions.

"Considering that the use of VX nerve agent endangers the safety at airports, effective countermeasures should be taken against such offenses in accordance with relevant international conventions," Yun told the conference.

"And now is the time, I believe, for us to seriously consider taking more fundamental measures on their membership in relevant regional and international forums including the UN as well as the CD," he added.

Seoul's push to diplomatically isolate the North will likely need more policy coordination with the US. Against this backdrop, media reports said that US Secretary of State Rex Tillerson will visit South Korea later this month as part of his Asian tour that will bring him to China and Japan as well.

Observers say that Yun and Tillerson might discuss Washington re-designating the North as a state sponsor of terrorism. In January, a US lawmaker introduced a bill calling for North Korea to be put back on the terrorism list.

Appearing in a TV news program on Sunday, Yun emphasized that Kim's death would speed up the US move to place Pyongyang on the terror list. (Yonhap)