Ms Kim Yo Jong, the only sister of North Korea's supreme leader Kim Jong Un, is now setting the tone of the country's foreign policy. And if he is young and belligerent, she is younger and more belligerent still.

Early this month, after human rights activists in South Korea used balloons to send anti-North propaganda leaflets across the border, Ms Kim called them "human scum" and "mongrel dogs". She faulted President Moon Jae-in of South Korea for failing to stop them and upbraided him for "putting his neck" into the "noose of pro-United States flunkeyism". She also threatened to move troops into border regions that have been demilitarised. But they weren't. Last Wednesday, Mr Kim halted those plans - at least for the moment.