North Korea says it has test-fired new multiple rocket launcher shells, a development which comes as the country is believed to be improving its conventional weaponry.

The North's Academy of Defence Science announced through state-run media on Monday that it "succeeded in developing new controllable shell and ballistic control systems for multiple rocket launchers."

The academy said the test was conducted on Sunday to evaluate their accuracy and that it demonstrated their advantages.

Photos released by the media show what North Korea claims to be 240 millimeter-caliber shells being fired from a mobile launch pad and hitting an island.

South Korea has said in a defense report that 240 millimeter-caliber rocket shells could be used for large-scale surprise attacks on Seoul and its surrounding regions.

North Korea apparently wants to highlight progress in its five-year defense plan, now in its fourth year, under which it researches and develops advanced weapons.