North Korea has called the test of two new missiles on Thursday a "solemn warning" against what it described as "South Korean warmongers".
The short-range missiles were fired into the Sea of Japan, also known as the East Sea, from Wonsan on North Korea's east coast.
Leader Kim Jong-un said his country was forced to develop weapons to "eliminate potential and direct threats".
He said the test involved a new tactical guided weapons system.
Mr Kim's comments, reported in state media, come after the North criticised a decision by South Korea and the US to hold military drills next month.
North Korea has long regarded the drills as preparation for an invasion.
Though the US and South Korea have refused to cancel the annual military exercises, they have been scaled back significantly.
South Korea's Joint Chiefs of Staff (JCS) said one of the new missiles travelled about 690km (428 miles). The US also confirmed that the missiles were "short-range".
The short range missile test yesterday puts the whole of the peninsula within range of a strike. Then there is the accusation that Seoul is "double dealing" - seeking peace while procuring new weapons and taking part in joint military drills with the US.
This language might sting a little after the South Korean President Moon Jae-in has worked so hard to develop a relationship with Kim Jong-un. Even Seoul's offer to send rice to the impoverished North appears to have been spurned for now.
North Korea may be trying to test its influence over the South. It's also a way of perhaps trying to split the positions of Washington and Seoul.