Russia''s Defense Ministry confirmed on Monday that North Korea had conducted a nuclear test and said it would thoroughly study its data.

North Korea earlier said it had conducted a successful underground nuclear test on May 25 "as part of the measures to bolster up its nuclear deterrent for self-defense."

"According to our data, North Korea indeed conducted a nuclear test in the northeast of the country on Monday morning," a ministry''s spokesman told RIA Novosti.

"We are studying the information received," the official said.

The Russian Foreign Ministry earlier expressed concern over North Korea''s announcement on its second nuclear test since the withdrawal from the Nuclear Non-Proliferation Treaty (NPT).

Pyongyang withdrew from the NPT in 2003 and conducted its first nuclear test in October 2006

"The information on North Korea''s nuclear test causes concern but before we draw any final conclusions it should be thoroughly checked," the ministry''s press service said in a statement.

Various geological survey agencies around the world said they had detected a 4.7-magnitude quake in the area where the test site is believed to be located.

Russia''s ambassador to the United Nations, Vitaly Churkin, said the UN Security Council would hold an emergency meeting later today in the wake of the test.

Meanwhile, South Korea''s Yonhap news agency reported that following the nuclear test on Monday Pyongyang test-fired a ground-to-air missile with a range of 80 miles (130 kilometers) from its northeastern Musudan-ri launch site.

The reclusive communist regime had been threatening for several weeks to resume work at its Yongbyon nuclear facility, which produces weapons-grade plutonium, after withdrawing from six-nation talks. The move came in response to international condemnation of an April 5 rocket launch, which Pyongyang said was carrying a communications satellite.

North Korea also said it would conduct further nuclear tests and rocket launches to ensure its security and defense capability.