North Korea has yet to finish developing 300-millimeter-caliber multiple rocket launchers, South Korea's defense ministry said Monday, following the North's provocative launches of missiles and artillery shells over the weekend.

North Korea fired a short-range projectile into the East Sea on Sunday, a day after shooting three other similar projectiles, presumed by Seoul to be missiles or rockets, off the Korean Peninsula's east coast in defiance of the international community's warnings against hostile actions.

The ministry presumed the projectiles to be modified KN-02 guided missiles or rockets fired from 300 mm-caliber multiple rocket launchers, given that they have a range of about 120 kilometers, long enough to reach regions far below the capital city of Seoul in the South.

The North, however, may not have the large-caliber rocket artillery system ready for a real combat situation yet, ministry spokesman Kim Min-seok said in a briefing.

"It is likely that they are in the stage of developing it," Kim said.

China and Russia have completely or partly developed the large-caliber rocket artillery system, but the North seems to have yet to finish the development, being conducted on technology possibly borrowed from the two countries, Kim said.

Following Saturday's launchings, the ministry first said the North fired three short-range guided missiles but renamed them as projectiles on Sunday on the assumption that the four, including the one fired on Sunday, may include missiles and rockets.

"Whether they are missiles or rockets, a sharp increase in the target range allows the North to aim at more objects and targets,"

Kim said. "An increase in the size of caliber means larger explosiveness and increased threats."

The unexpected launches by the North came amid nagging inter-Korean tensions, triggered after the North's long-range rocket launch in December and its third nuclear test on Feb. 12.

The Unification Ministry, which is in charge of dealing with North Korean affairs, called the North's weekend launches "deplorable," demanding that the North "act responsibly." (Yonhap News)