North Korea has fired several short-range projectiles into the sea off the country's east coast.
South Korean officials say the projectiles were launched Monday from the eastern city of Hamhung.
The officials did not say what type of missiles or rockets may have been fired.
Last week South Korean officials said the North fired medium-range missiles into the sea in defiance of U.N. sanctions.
North Korea has been threatening for weeks to initiate preemptive nuclear strikes against Washington and Seoul to protest South Korea-U.S. military drills. The North sees the drills as a rehearsal for a military invasion.