Pyongyang has conducted six weapons tests since the start of the year, including hypersonic missiles, one of the most intense barrages in a calendar month on record, while ignoring US offers of talks.

This week, it "conducted the test-fire for updating long-range cruise missile system and the test-fire for confirming the power of conventional warhead for surface-to-surface tactical guided missile," the official Korean Central News Agency said.

KCNA said the Tuesday test involved long-range cruise missiles flying over the East Sea -- also known as the Sea of Japan -- and hitting "the target island 1,800 km away."

Thursday's launch then saw short range ballistic missiles hit a "target island", KCNA added, "proving that the explosive power of the conventional warhead complied with the design requirements."

The flurry of sanctions-busting tests this month come after Kim re-avowed his commitment to military modernisation at a key party speech in December.

Washington imposed new sanctions in response, prompting Pyongyang to double down on weapons testing and hint last week that it could abandon a years-long self-imposed moratorium on nuclear and long-range tests.

Kim also visited a munitions factory that produces "a major weapon system", KCNA said.

In a photograph released by the news agency, a beaming Kim, wearing his usual long black belted leather jacket, is seen surrounded by uniformed officials.

Kim "highly appreciated the factory effecting collective innovation and leaping progress in producing major weapons," KCNA reported.

The string of tests comes at a delicate time in the region, with Kim's sole major ally China set to host the Winter Olympics next month and South Korea gearing up for a presidential election in March.

Domestically, North Korea is preparing to celebrate the 80th anniversary of the birth of late leader Kim Jong Il in February, as well as the 110th birthday of founder Kim Il Sung in April.