SEOUL (Reuters) – North Korea demanded on Thursday the handover of “terror suspects” who plotted to kill leader Kim Jong Un with a biochemical substance, repeating accusations it made last week that U.S. and South Korean spies were behind the plan.

The North’s KCNA news agency last week accused the U.S. Central Intelligence Agency and South Korea’s National Intelligence Service of a plot to assassinate its “supreme leadership” with a biochemical weapon.

Tension on the Korean peninsula has been high for weeks, driven by concern that North Korea might conduct its sixth nuclear test or test-launch another ballistic missile in defiance of U.N. Security Council resolutions.

“The Central Prosecutor’s Office will ask for the handover of those criminals and prosecute them under the relevant laws,” North Korean vice foreign minister Han Song Ryol told foreign diplomats and reporters in Pyongyang, China’s Xinhua news agency reported.

The CIA and the U.S. White House declined to comment on the statement from the North’s Ministry of State Security last week.

The South Korean intelligence service said the charge was “groundless”.

Han “declared the principled stand of the … government to find out all of the terrorist maniacs and mercilessly wipe them out”, the North’s KCNA news agency said in a report on the briefing.

There was no elaboration in either the Xinhua report or the KCNA report on how many suspects North Korea was seeking, or of who or where they were, but Xinhua said North Korea had vowed to “hunt down to the last one of the suspects in every corner of the earth”.

Separately, the CIA said on Wednesday it had established a Korea Mission Center to “harness the full resources, capabilities and authorities of the Agency in addressing the nuclear and ballistic missile threat posed by North Korea”.

The center would gather experienced officers from across the CIA in one entity “to bring their expertise and creativity to bear against the North Korea target”, it said.

(This version of the story adds dropped word “no” in paragraph eight.)

(Reporting by Jack Kim; Editing by Robert Birsel)