A new North Korean missile launch site under construction is designed to fire rockets even more advanced than those already capable of reaching the western U.S., South Korea said Tuesday.

South Korean Defense Minister Lee Sang-hee told parliament that construction on the new site on North Korea's west coast began eight years ago and is about 80 percent complete.

The site in the village of Dongchang-ni appears to be designed to launch "a bigger-sized missile or satellite projectile" than rockets deployed from the North's east coast facility.

North Korea's clandestine missile program has been a key regional concern, along with its nuclear weapons program.

The country has some 200 "Nodong" missiles with a range of about 800 miles - far enough to reach Japan - and more than 600 Scud-type, short-range missiles that could reach South Korea.

In 2006, the North launched a long-range missile, the Taepodong-2 - considered the country's most advanced rocket - from its east coast site in Musudan-ni. The missile has a range of more than 4,160 miles, putting the western U.S. into striking range, according to the South Korean government.

Experts say the missile has a small payload and is unlikely to be accurate and the 2006 test was considered a failure: The rocket plunged into the ocean shortly after liftoff.

Later that year, the communist nation conducted an underground nuclear test in 2006. North Korea is believed to have enough plutonium to produce about half a dozen bombs but experts say it has not acquired the technology needed to mount a nuclear weapon on a missile.

Earlier this year, North Korea tested the engine of a long-range missile at the new, western missile site, U.S. and South Korean officials said. That missile is not believed to bear longer-range capability.

But the engine test - considered as a key step toward a development of a new missile - could confirm that the North actively is working on developing its long-range missile program.

The test is a critical facility for measuring vibration from the engines and adjusting guidance systems to account for it, which can help make missiles more accurate.