North Korea has recently launched a submarine capable of firing ballistic missiles, a news report said Sunday, adding to concerns over the evolving missile and nuclear threats posed by the communist country.

Pyongyang imported, reverse-engineered and modified a Soviet-era Golf-class diesel submarine that was built in 1958 and decommissioned in 1990, Yonhap reported, citing an unnamed government source. The regime is believed to have bought the vessel in the early 1990s.

“The new submarine is 67 meters long with a beam of 6.6 meters, and has a dived displacement in the 3,000-ton range,” the source was quoted as saying.

The report is the latest in a recent flurry of articles at home and abroad on the North’s submarine technology.

But Seoul’s military officials expressed skepticism that it has acquired the capability to deploy submarine-launched ballistic missiles, or SLBMs.

The Russian 3,500-ton Golf II class submarine carries the R-21 SLBM, a single-stage, liquid-propellant missile with a 1,180-kilogram warhead that has a maximum range of 1,420 kilometers.

The newly built submarine is identical to the one detected at the Sinpo South Shipyard by the U.S.-Korea Institute at Johns Hopkins University through satellite imagery and released last month on its website, 38 North, according to the Yonhap source.

Located in South Hamgyong Province on the country’s east coast, the dockyard houses the headquarters of its Maritime Research Institute of the Academy of National Defense Sciences and serves as its chief submarine manufacturing facility.

The heavily militarized country has conducted multiple tests both on the ground and at sea to master the technology of mounting a missile tube on the new vessel, another source was quoted as saying. It is expected to take at least one or two years before the completion of the tests.

Last week, arms expert Joseph Bermudez Jr. said on 38 North that Pyongyang had built “a new test stand” at Sinpo for a possible vertical launch of SLBMs. He said that the installation had a 35-by-30-meter concrete pad with an about 12-meter-high test stand.

The North is believed to have some 70 submarines, about 20 of which are the 1,800-ton Romeo-class and about 40 of which are the 325-ton Sangeo-class vessels. Though old and equipped with outdated weapons, they outnumber the South’s submarines.

A SLBM-deployed submarine would pose a grave threat to the South. Experts consider strategic bombers, intercontinental ballistic missiles and SLBMs to be the components of a “nuclear triad” needed to ensure a nation’s nuclear deterrence.

Seoul has been seeking to beef up its antisubmarine capabilities since a North Korean submarine torpedoed its corvette Cheonan in the West Sea in March 2010, killing 46 sailors. Pyongyang denies responsibility.

By Shin Hyon-hee (heeshin@heraldcorp.com)