North Korea fired two suspected short-range ballistic missiles on Monday from an airport in its capital Pyongyang, according to South Korea's military.It's the fourth test in less than two weeks, an unusually rapid series of launches as the country demonstrates its expanding missile arsenal. South Korea's Unification Ministry urged North Korea to choose peace over its missiles.Japan also reported the launch - its Defense Minister saying the missiles appeared to have landed in the ocean near North Korea's east coast. Chief cabinet secretary Hirokazu Matsuno condemned the incidentas a threat to peace and security."The recent actions of North Korea, including repeated launches of ballistic missiles in the past, are a threat to the peace and security of Japan and the region, as well as the international community. We strongly condemn those actions."Two of Pyongyang's recent launches involved 'hypersonic missiles', capable of high speed and maneuvering after take-off.A test on Friday involved two short-range ballistic missiles fired from train cars.These appeared to bedesigned to evade missile defenses.The North also vowed to pursue tactical nuclear weapons which could allow it to deploy nuclear warheads on those missiles.U.S. President Joe Biden's administration imposed its first new sanctions on Pyongyang on Wednesday.It also repeated calls for North Korea to return to denuclearisation talks.But Pyongyang defended the tests as its right to self-defense.It added on Friday that Washington was still engrossed in its policy of what it called 'isolating and stifling' North Korea."