The sister of North Korea’s leader, Kim Jong-un, has condemned South Korea as a “frightened dog barking” after Seoul protested against a live-fire military exercise by the North.

Kim Yo-jong’s comments – her first known official statement – came after Seoul’s security ministers expressed “strong concern” over Pyongyang’s firing of two short-range ballistic missiles on Monday – its first weapons test for more than three months.

In the statement published by state media on Tuesday, Kim Yo-jong said the North was entitled to carry out military drills and dismissed the South’s condemnation as a “truly senseless act”.

“Such incoherent assertion and actions … only magnify our distrust, hatred and scorn for the South side as a whole,” she added.

Kim has long been one of her brother’s closest advisers and has frequently been pictured alongside him. She acted as her brother’s envoy to the South during the Pyeongchang Winter Olympics in 2018, which ushered in a rapid diplomatic rapprochement on the divided peninsula.

Kim did not mention South Korea’s president, Moon Jae-in – whom she met several times – but described Seoul’s presidential office, the Blue House, as “a burnt child dreading fire”.

The publication of a political statement in her own name highlights her central role in the regime, analysts said.

“By having someone like Kim Yo-jong – who has been a dovish figure towards the South and acting as a soft and friendly messenger – issue such a strong statement condemning the current government, the North is raising its pressure,” said Go Myong-hyun, an analyst at the Asan Institute for Policy Studies.

Kim was named in January as a first vice-department director of the central committee of the ruling Workers’ party, but the new statement signalled she may have moved further up the hierarchy, he added.

Earlier on Tuesday, North Korean state media published pictures of Kim Jong-un supervising what it called a “long-range artillery” exercise.

Monday’s drills came days after the one-year anniversary of the failed Hanoi summit between Donald Trump and Kim Jong-un, and followed the expiry of an end-of-year deadline Pyongyang set Washington to offer it fresh concessions.

The two countries are deadlocked over sanctions relief and what the North would be willing to give up in return, and there are no significant contacts between the North and South.

Kim Jong-un has declared the North no longer considered itself bound by its moratoriums on nuclear and intercontinental ballistic missile tests, and threatened to demonstrate a “new strategic weapon” soon.

Seoul and Washington last week postponed forthcoming joint military exercises over the coronavirus outbreak – the South has more than 5,000 infections – and the South’s president, Moon, offered to cooperate over the disease with the North, which has closed its borders to try to prevent a potentially devastating outbreak.﻿