Pyongyang has conducted six weapons tests in January, including hypersonic missiles, one of the most intense barrages in a calendar month on record, as it doubles down on Kim's military-boosting plans and ignores US offers of talks.

The official Korean Central News Agency 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 two "tactical guided 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.

On Friday, KCNA ran photographs showing Kim, wearing his usual long black belted leather jacket, surrounded by uniformed officials -- their faces pixelated out -- inspecting a munitions factory that produces "a major weapon system".

Kim said he "highly appreciated" the factory's role in modernising his weapons programme, KCNA reported.

He said "the factory holds a very important position and duty in modernizing the country's armed forces," it added.

KCNA did not mention Kim attending the weapons tests this week, but a separate state media report said he inspected a vegetable farm in the Ryonpho area of Hamju county, which is close to the site of the Thursday test.

- Signs of progress -

The January launches are all part of North Korea's five-year weapons development plan to "upgrade its strategic arsenal," Hong Min of the Korea Institute for National Unification in Seoul told AFP.

"The cruise missiles fired Tuesday are an extension of the same type of missiles fired from last September with improvements in distance and speed," he said.

The string of tests are also a response to South Korea's own efforts to upgrade its weapons systems, with successful tests in 2021 of supersonic and new submarine-launched ballistic missiles, he said.

"The North is showing it's also developing missiles to counter what the South has on its hand," he added.

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.

The need to celebrate such "prominent anniversaries" helps explain the recent string of tests, said analyst Ankit Panda.

"We should expect a bumpy first half of the year," he told AFP.

He said it was also possible that Covid concerns had forced North Korea to modify its usual winter training schedule, prompting a shift to missile testing to ensure "positive propaganda" on national defence domestically.

"This could be all the more important at a time when the national economy is doing poorly and agricultural output may threaten famine-like conditions," he added.

The impoverished North, reeling economically from a self-imposed coronavirus blockade, has recently restarted cross-border trade with China.