The unidentified source said North Korea's alleged use of a Russian-made AN-2 aircraft came after South Korean officials doubted the old aircraft could be used for missile launches, the Yonhap News Agency reported.

"I wonder if that is technically possible," South Korean Defense Ministry spokesman Won Tae-jae said.

"It is just technically not possible for the small AN-2 to lift off while carrying 2-ton missiles and to fire them in air," an unidentified Air Force official concurred. "It is simply impossible to equip an AN-2 with the Styx missiles as its wings are only a few feet from the ground."

Details regarding Tuesday's missile tests have yet to be confirmed, leaving officials to question whether the Russian plane was used to launch the missiles or if a ship was responsible for the test.

Yonhap said, according to sources, North Korea has deemed the West Sea a no-entry area until next Wednesday.