North Korea says its leader Kim Jong Un has supervised the test-firing of shells produced by the country's newly established military firm.

The ruling Workers' Party newspaper Rodong Sinmun said on Friday that Kim observed the test-firing of 240-millimeter shells from a multiple rocket launcher the previous day.

The paper says the shells were developed by a new national defense industrial enterprise set up under the Second Economy Commission responsible for the country's munitions industry.

The article has a photo of a shell being fired from the mobile rocket launcher.

Kim reportedly praised the shells and stressed the need for the national defense industrial enterprise to carry out the munitions production plan for this year without fail.

South Korea's Yonhap News Agency quotes observers as saying North Korea appears to be stepping up the development of rocket launcher shells in a bid to supply them to Russia for its invasion of Ukraine.

On Monday, North Korea test-fired what it called "super-large rocket shells" that are believed to be short-range ballistic missiles. The South Korean military said the North wants to display their capabilities and may hope to export them.