North Korea has fired three short-range projectiles into the waters off its east coast, a South Korean defence official said.
The move was most likely a routine test-firing, but the official said it could also be meant to stoke tensions with Seoul.
The official said the projectiles flew about 120 miles before harmlessly landing in the water. They were fired from North Korea's eastern port city of Wonsan, and the South Korean military is investigating the type of projectiles and the North's intentions.
Short-range test firings by North Korea are not unusual, but a barrage of missile and artillery tests earlier this year boosted animosity between the rivals.
North Korea has in recent months threatened South Korea's leader, and the South has vowed to hit the North hard if provoked.
North Korea's rising anger coincided with annual joint military exercises by the US and South Korea and a visit to Seoul by US President Barack Obama. North Korea also test-fired two medium-range ballistic missiles and exchanged artillery fire with South Korea near a disputed boundary in the Yellow Sea.
There is also widespread speculation about a possible North Korean nuclear test. North Korea has conducted three nuclear tests since 2006, the latest in February 2013.
Experts believe North Korea has developed a handful of crude nuclear devices and is working towards building a warhead small enough to mount on a long-range missile, although most experts say that goal may take years to achieve.