North Korea test-launched hypersonic missiles in Pyongyang the previous day that successfully struck targets in the East Sea, with leader Kim Jong-un in attendance, state media reported on Monday.
Leaders of South Korea and Japan are going to meet in order to discuss the recalcitrant regime's evolving threats and other shared challenges
This comes a day after the US and South Korea staged combined air drills, involving at least one B-1B strategic bomber, on Sunday.
Japan's defence ministry described the projectiles as "ballistic missile-like" but they did not come down in the country's exclusive economic zone.
It noted that the South Korean military was closely monitoring relevant situations and maintaining defence posture in preparation for possible additional launches.
The move marks a significant escalation from the short-range tests Pyongyang conducted since May.
The South Korean navy said in a statement that it would stage the "territory defense exercises" in the East Sea from Sunday to Monday.
Saturday's firings marked the seventh round of such launches since July 25 when the North broke a 17-month hiatus and started firing missiles and projectiles to test new weapons and protest the South-US joint military exercise that it has long denounced as a rehearsal for invasion.
Kim guided the test of fire of a new weapon again on Friday morning
North Korea "fired a number of short-range projectiles from its Hodo peninsula near the east coast town of Wonsan to the northeastern direction from 9:06 am (0006 GMT) to 09:27 am today", the South's Joint Chiefs of Staff said in a statement.
