The South Korean government has concluded that the six missiles North Korea launched into the sea between Saturday and Monday aimed to test new bigger multiple rocket launchers.

The missiles flew about 150 km, but their maximum range is estimated to be 180-200 km, a South Korean government official said Tuesday.

Until now the North was believed to have three kinds of multiple rocket launchers -- 107 mm, 122 mm, and 240 mm with a maximum range of less than 65 km.

But the new launchers could threaten South Korean military headquarters at Gyeryongdae in South Chungcheong Province and U.S. bases in Pyeongtaek and Osan, both in Gyeonggi Province, as well as the entire Seoul region.

With six to 12 launch tubes, mobile rocket launchers can fire more projectiles -- eight or nine rockets in 10 minutes -- than missile launch vehicles.

The launchers are difficult to detect until they start firing.

"South Korean and U.S. authorities concluded that they were multiple rocket launchers rather than short-range missiles given their launch speed, trajectory, and the shape the vehicles," the official said.

But the official added it is unlikely the new launchers have been deployed warfare-ready.

The test launches could be construed as provocative, although they "do not necessarily violate North Korea's international obligations," Pentagon spokesman George Little told reporters Monday.

Meanwhile, the U.S. test-launched an intercontinental ballistic missile dubbed Minuteman 3 on Tuesday, about a month after it decided to postpone the test in consideration of rising tensions on the Korean Peninsula.

On Saturday, North Korea denounced the Minuteman test as a "military provocation." With a range of 13,000 km, the missile has three W-68 170-kiloton nuclear warheads, each of which can strike a different target.

