North Korea on Monday morning fired two ballistic missiles into open waters in the East Sea without proclaiming a no-sail or no-fly zone to protect civilian vessels or planes.
Seoul called the launches a "provocative act posing a serious threat to international flights and navigation and civilian safety."
The Defense Ministry here is considering a complaint to the UN since the firing violates a UN Security Council resolution banning the North from launching all ballistic missiles.
"The North fired two ballistic missiles in a northeasterly direction from its Kitdaeryong base in Anbyon, Kangwon Province," a ministry official said. "They flew about 500 km and fell into open waters within Japan's air defense identification zone.”
A military source speculated they were either Scud-D or Scud-ER missiles.
On Feb. 21, the North fired several projectiles into the East Sea that are believed to have come from new multiple rocket launchers. Experts here believe Pyongyang is steadily increasing the range of such rockets.
The government and military here believe the latest launches were a protest against ongoing South Korea-U.S. military drills.
They are alarmed that the rockets were fired without any advance signs like movements of launchers or the declaration of a no-fly or no-sail zone.
The joint drills come to a close this week but will be immediately followed by a combined field training exercise involving a U.S. nuclear-powered submarine navigating in waters off the Korean Peninsula.
Military authorities have stepped up surveillance of the North because they believe the chances of more provocations are high.
"The North still seems to be attempting to pressure the South into concessions, so it's hard to be optimistic about the future of inter-Korean relations," said Prof. Yoo Ho-yeol of Korea University.