North Korea threatened on Wednesday, June 28 to "impose the death penalty" on the South's former president Park Geun-Hye over an alleged plot to assassinate its leader Kim Jong-Un, AFP reports.

Park had "pushed forward" a supposed plan by Seoul's intelligence services to eliminate the North's leadership, Pyongyang's security ministry and prosecutors said in a statement carried by its official Korean Central News Agency.

"We declare at home and abroad that we will impose death penalty on traitor Park Geun Hye," it said.

The former director of South Korea's National Intelligence Service (NIS) Lee Byung-Ho would meet a similar fate, it added.

They "can never make any appeal even though they meet miserable dog's death any time, at any place and by whatever methods from this moment".

The declaration comes after the killing of Kim's estranged half-brother Kim Jong-Nam by two women using the banned nerve agent VX at Kuala Lumpur international airport in February.

Both Malaysia and South Korea have blamed the North for the assassination, which retorts that the accusations are an attempt to smear it.

Last month Pyongyang's powerful ministry of state security said it had foiled a plot by the US and South Korean spy agencies to kill Kim using a biochemical weapon.