The North Korean leader praised the country's efforts to prevent any COVID-19 outbreak.
Pyonyang is expected to test the larger missile in coming months, sending a message to both Trump and Biden.
"Not something groundbreakingly new".
Who is Kim Yo-jong?
The North Korean leader has only been seen in public a handful of times this year.
A source said Kim Jong Un believed pet dogs represent Western "decadence".
Its past six nuclear tests likely helped it develop miniaturised nuclear devices.
The undeclared facility is now part of Kim Jong-un's nuclear weapons programme, researchers say.
Seoul’s Unification Ministry said the building was destroyed on Tuesday afternoon.