North Korea has test-fired a series of missiles in an apparent act of defiance on 4 July, American Independence Day.
South Korea's Joint Chiefs of Staff say up to seven Scud-type missiles were fired from one of the North's east coast launch sites on Saturday, with a range of about 500km.
The distance the rockets travelled indicates they were ballistic missiles. All landed in the Sea of Japan, known in South Korea as the East Sea.
South Korea and Japan have called the latest tests, which follow several others in recent weeks, an "act of provocation".
North Korea is barred by United Nations resolutions from firing ballistic missiles and the latest launches have further stoked regional tensions already high due to its second underground nuclear test on 25 May.
In June, the UN Security Council approved a resolution to ban the trade of weapons by North Korea, including missile systems.
It also authorised UN member states to inspect North Korean sea, air and land cargo, requiring them to seize and destroy shipped goods that violate the sanctions.
If the latest launches were the ballistic Scuds, it would mark an escalation by the North, which has fired several non-ballistic, short-range missile since the nuclear test.
Pyongyang test fired four similar missiles earlier in the week, and fired a rocket in April in what was widely viewed as a long-range missile test.
The latest tests are of more concern, because the rockets have a much longer range.
