Kim Jong Un's sister promised to build what she called "overwhelming and the most powerful military power" to protect North Korea and peace in the region.

That's according to the North's KCNA news agency quoting her on Wednesday.

Kim Yo Jong pointed to the U.S. military's exercises around the Korean peninsula this year, particularly live-fire drills with the quote "South Korean puppet military gangsters", as making the security situation in the area dangerously unstable, Reuters reported. 

The US and South Korea's annual joint drills this year were held at a greater scale and intensity than the year before, part of a pledge by their leaders to upgrade their military readiness against the North.

The South's military says around 100 military aircraft carried out a two-week-long drill this month.

While Washington and Seoul claim the drills are defensive and conducted regularly to maintain readiness, Pyongyang insists U.S. military exercises are preparations for a nuclear war against it.

Earlier this month, the North's KCNA news agency reported Kim Jong Un saying now is the time for North Korea to be more prepared for war than ever, citing what he called unstable geopolitical situations surrounding his country.