N. Korea shows possible signs of preparing for nuclear test: 38 North

Fresh satellite imagery shows signs of North Korea preparing for a nuclear test, a U.S. website monitoring the communist nation said Friday.

The May 5 imagery of the North's Punggye-ri underground nuclear test site showed vehicles at what is believed to be the test command center, though the test site continues to show low levels of activity, the website 38 North said.

"While the historical record is incomplete, it appears that vehicles are not often seen here except during preparations for a test," 38 North said. "No vehicles or people were observed at this facility on imagery from May 2. However, what appears to be four closely-parked vehicles are present on May 5."

Concerns have persisted that the North could carry out its fifth nuclear test around the Workers' Party Congress that opened Friday for the first time in 36 years. North Korean leader Kim Jong-un is expected to use the meeting to publicize achievements to further solidify his grip on power.

In recent months, Pyongyang has made a series of claims of breakthroughs in its nuclear and missile programs, including miniaturizing nuclear warheads to fit on an ICBM, mastering missile atmospheric re-entry technology and developing a solid-fuel rocket engine.

The North has also conducted a series of weapons tests, including a series of test launches of the Musudan intermediate-range mobile missile and the firing of a submarine-launched ballistic missile (SLBM). (Yonhap)