The Democratic People's Republic of Korea (DPRK) said Friday that it successfully conducted a nuclear warhead explosion test at the northern nuclear test ground, the fifth by the country since 2006.

The test aimed to judge the power of a newly developed nuclear warhead, said the DPRK Nuclear Weapons Institute.

"This is definitely a higher level of DPRK's technology of mounting nuclear warheads on ballistic rockets," the official KCNA news agency quoted the institute as saying in a statement.

The test "examined and confirmed the structure and specific features of the movement of a nuclear warhead that has been standardized to be mounted on strategic ballistic rockets of the Hwasong artillery units" of the strategic force of the Korean People's Army, said the statement.

Factors measured in the test include "explosion might, nuclear material use coefficient," the statement said. The test had no radioactivity leakage or adverse impact on the surrounding environment, it added.

The statement also said that the DPRK is now able to produce "a variety of smaller, lighter and diversified nuclear warheads of higher strike power as many as it wants."

The nuclear warhead test was "part of practical countermeasures" to the threat from the United States, the statement said, adding that the DPRK would take further measures to "bolster the country's nuke power in quality and quantity" so as to protect itself from U.S. threats.

The nuclear test coincided with the 68th anniversary of the founding of the country.

The DPRK confirmed the nuclear test after various seismic-monitoring agencies reported an earthquake in the country.

Earlier in the day, the China Earthquake Network Center said a magnitude-5.0 earthquake jolted the DPRK at 0030 GMT at a depth of 0.0 km.

Meanwhile, the European Mediterranean Seismological Center said a magnitude-5.0 earthquake was detected in the DPRK and later revised the magnitude to 5.3. The U.S. Geological Survey saw the tremor as a magnitude-5.3 quake.

The nuclear test is a second in eight months, after a test of the country's first H-bomb. The DPRK also conducted underground nuclear tests respectively in 2006, 2009 and 2013.

On Tuesday, the KCNA reported that top DPRK leader Kim Jong Un has instructed to "continue to make miraculous achievements in bolstering up nuclear force one after another in this historic year," giving a hint that another nuclear test may be in the pipeline.

The DPRK's nuclear tests run counter to relevant UN Security Council resolutions and to the goal of denuclearization of the Korean Peninsula.