President Donald Trump declared North Korea a state sponsor of terror and promised new sanctions at the "highest level".

Mr Trump cited Pyongyang's nuclear ambitions and assassinations carried out on foreign soil for the decision.

Additional sanctions were expected to be announced by the US Treasury on Tuesday.

US officials highlighted the killing of North Korean leader Kim Jong-un's estranged half brother Kim Jong-nam at Kuala Lumpur airport in February as an assassination on foreign soil. He was sprayed with a nerve agent.

They also said the death of US student Otto Warmbier, who died of injuries suffered in North Korean custody, constituted terrorism.

Mr Trump, speaking at the White House, said: "In addition to threatening the world by nuclear devastation North Korea has repeatedly supported acts of international terrorism including assassinations on foreign soil. North Korea must end its unlawful nuclear and ballistic missile development.