SEOUL: North Korea fired two more ballistic missiles off its east coast on Monday, as the powerful sister of leader Kim Jong Un warned U.S. forces to halt military drills, saying the reclusive nuclear state could turn the Pacific into a "firing range".

The launches come just two days after North Korea fired an intercontinental ballistic missile (ICBM) into the sea off Japan's west coast, prompting the United States to hold joint air exercises with South Korea and separately with Japan on Sunday.

North Korea's state media confirmed it fired two projectiles from a multiple rocket launcher, aiming at targets 395 km (245 miles) and 337 km (209 miles) away, respectively.

"The 600mm multiple rocket launcher mobilised in the firing... is a means of tactical nuclear weapon," capable of "paralysing" an enemy airfield, state news agency KCNA said.

Japan's Defense Ministry said the two missiles, fired around 2200 GMT, reached a maximum altitude of about 100 km and 50 km, and fell outside Japan's EEZ.

South Korea's Joint Chiefs of Staff said the missiles flew 390 km and 340 km and strongly condemned the launches as a "grave provocation" that should be ceased immediately.

"We will maintain solid readiness posture based on security cooperation with the United States and Japan and our ability to overwhelmingly respond to any provocations by North Korea," it said in a statement.

Seoul's foreign ministry announced sanctions on four individuals and five entities linked to Pyongyang's weapons programmes on Monday, including one South African national and two Singaporean shipping firms.

The U.S. Indo-Pacific Command said the latest launch does not pose an immediate threat but highlight the "destabilising impact" of the isolated country's unlawful weapons programmes.

U.N. spokesman Stephane Dujarric urged Pyongyang to "immediately desist from taking any further provocative actions" banned under Security Council resolutions, and resume denuclearisation dialogue.

TENSIONS RISING

North Korean leader Kim's sister, Kim Yo Jong, warned against increased presence of U.S. strategic assets following the joint air drills with its Asian allies over the weekend.

"The frequency of using the Pacific as our firing range depends upon the U.S. forces' action character," she said in a statement carried by KCNA.

Analysts say tensions are likely to flare as South Korea and the United States are set to hold simulated nuclear tabletop exercises aimed at improving operations of American nuclear assets this week and annual springtime Freedom Shield field training field training in March.

"Tension on the peninsula is likely to reach its peak in coming months as North Korea is accelerating its military actions with higher frequency, and her statement indicates that it would continue impromptu missile tests using the Pacific as its shooting range," said Yang Moo-jin, a professor at the University of North Korean Studies in Seoul.

Park Won-gon, a professor at Ewha Womans University in Seoul, said Monday's missile launch and statement are in line with the North Korean foreign ministry's recent threat to take "unprecedentedly persistent, strong" responses to the allies' joint military drills.

"North Korea seems to be trying to reinforce its nuclear capability by raising issue over the drills, and the statement by Kim Yo Jong signals there would be additional provocations," Park said.

Monday's missile launch is the North's third known weapons test this year after it fired an unprecedented number of missiles last year, including ICBMs capable of striking anywhere in the United States.

Kim Yo Jong also criticised some South Korean experts' assessment of its missile capabilities that it took over nine hours for the "sudden" missile launch to take place following an order from leader Kim, and said South Korea didn't even fly reconnaissance planes at the time of its launch.

"We have possessed satisfactory technology and capability and, now will focus on increasing the quantity of their force," she said. "We affirm once again that there is no change in our will to make the worst maniacs escalating the tensions pay the price for their action."