"Russia definitely condemns the nuclear test by the DPRK" and the move "has caused huge damage to the process of nuclear nonproliferation," Russian President Vladimir Putin was quoted by the Itar-Tass news agency as saying.

The DPRK said on Monday that it had conducted a successful underground nuclear test, according to the official Korean CentralNews Agency (KCNA).

Putin told the Russian envoy to hold consultations on the test with the UN Security Council.

"I hope North Korea (DPRK) will return to the process of negotiations," he said.

Mikhail Kamynin, spokesman for the Russian Foreign Ministry, said on Monday that Russia was imperatively calling on the DPRK "to take steps, without further delay, to go back to the regime of the Nuclear Weapons Nonproliferation Treaty and to resume the six-nation negotiations."

Russia is now examining the ecological system in the region bordering the DPRK.

No seismic phenomena or radioactive consequences of the DPRK's underground nuclear test were recorded in the country's Far East, Russia's Far Eastern Regional Center of the Ministry for Emergency Situations reported.

No heightened radioactive background was recorded in Russia's Primorye Territory.

Ecologists in Primorye, however, are troubled by the nuclear test.

"All explosions of nuclear weapons are fraught with serious consequences. Most dangerous of all is lack of information. We do not know how successful or not was the test" in the DPRK, said Anatoly Lebedev, head of a public ecological organization.