North Korea’s third underground nuclear test last month was fueled by plutonium and was not a device that used enriched uranium, according to the Russian government.

Retired Col. Gen. Viktor Yesin, a consultant to the Russian Defense Ministry and former commander of strategic nuclear forces, told the Washington Free Beacon that Russia’s government had obtained new details of the Feb. 12 underground test.

Yesin said the North Koreans’ most recent test blast was "an implosion-type nuclear explosive device that used plutonium for fissile material."

Additionally, the test produced a larger nuclear yield than Pyongyang’s two earlier tests.

"In comparison to its previous nuclear tests of 2006 and 2009, this time North Korea tested a more powerful nuclear explosive device," Yesin said. "According to the Russian Ministry of Defense it had an estimated yield of 10 to 20 kiloton"—the equivalent of 10,000 to 20,000 tons of TNT, he said.

Yesin did not disclose how the Russian government was able to make the determination.

However, an intelligence source said the information was obtained by Russia’s SVR intelligence service, indicating it may have been provided by human agents rather than through technical means that can detect traces of radiation in the atmosphere after a test.

Yesin currently is a researcher at the state-run United States and Canada Institute of the Russian Academy of Sciences in addition to advising the Russian Defense Ministry on nuclear and strategic issues.

An official of Russia’s atomic energy agency said after the February nuclear test that Moscow no longer had "working relations" with North Korean nuclear engineers or technicians.

However, a North Korean scientist is known to work at Russia’s Joint Institute of Nuclear Research near Moscow. U.S. officials identified the scientist, Li Je Sen, as the North Korean.

Russia operates three regional Special Control Service laboratories that are part of the 12th GUMO of the Defense Ministry, the unit in charge of Russia’s nuclear forces. The Russians also operate nuclear monitoring sensors in the Eastern Military District.

The office of the director of national intelligence stated in a short announcement the day of the nuclear test that U.S. intelligence "assesses that North Korea probably conducted an underground nuclear explosion in the vicinity of Punggye on Feb. 12, 2013."

"The explosion yield was approximately several kilotons. Analysis of the event continues," the ODNI statement said.

An ODNI spokesman had no information beyond the statement issued Feb. 12.

U.S. intelligence officials said that despite multi-billion dollar sensors and other equipment devoted to foreign nuclear monitoring spy agencies have been unable to determine either the type of nuclear fuel used in the blast or its yield.

Intelligence agencies are trying to determine if the latest underground test used highly enriched uranium that would indicate the North Koreans have developed a second path to a nuclear weapon by producing enriched uranium for weapons. North Korea’s arsenal is known to be based on plutonium pits for its nuclear weapons.

The intelligence failure also is a setback for international nuclear monitoring efforts and the Obama administration’s plan for a second attempt at Senate ratification of the Comprehensive Test Ban Treaty, considered a high priority of the president’s arms control agenda during his second term.

The Comprehensive Test Ban Treaty Organization, a group based in Vienna, Austria, set up under the CTBT, said Tuesday that a month after the North Korean test it was unable to find proof of a nuclear test from radioactive traces normally vented into the air.

As a result, the agency has been unable to determine the type of fissile material used in the blast.

The CTBTO has a network of international monitoring stations and its sensors failed to detect any traces of the test.

"It is very unlikely that we will register anything at this point … at this late stage," CTBTO spokeswoman Annika Thunborg told Reuters News Agency.

One reason no traces of the test were detected is that North Korea may have taken steps to prevent venting in order to thwart international intelligence-gathering efforts.

A congressional aide said the test monitoring failure does not bode well for the administration’s efforts to seek Senate ratification of the test ban treaty.

"It's clear from even the CTBTO that they haven't collected the ‘smoking gun’ evidence of a test," the aide said. "Just like in 2009. It goes to show that CTBT was a bad idea in 1999—when the Senate defeated it—and it's a bad idea today."

The Senate voted down the treaty in 1999 after determining that the pact was not in the U.S. national security interest.

Due to a procedural move by Senate supporters, the treaty was withdrawn and thus can be ratified at a later time.

President Barack Obama and Vice President Joe Biden have said since 2008 that they plan to again seek Senate ratification of the CTBT.

Many Republicans however, are opposing the idea, as banning tests under a treaty increases the risks for the reliability of the U.S. nuclear arsenal as it begins to be cut to 1,550 deployed strategic warheads under the 2010 New START arms treaty and as the president plans to seek a further one-third warhead cut in negotiations with Moscow.

"We are confident that the system works very well," Thunborg said of CTBTO’s 270 monitoring stations.

According to U.S. officials, North Korea gave up plutonium production in 2007 under international pressure.

However, the North allowed visiting nuclear specialist Siegfried Hecker in 2010 to visit Pyongyang’s secret uranium enrichment facilities. The disclosure raised new concerns that the communist regime was running parallel nuclear programs to produce both plutonium and uranium cores for nuclear bombs.

North Korea recently ramped up threatening rhetoric against the United States and South Korea following the imposition of new United Nations sanctions on the country for its latest nuclear test.

The threats included warnings for the first time that the North will use nuclear-tipped missiles for strikes against the United States.

The regime also withdrew from the 1953 armistice with South Korea that ended hostilities during the Korean War and canceled a communications hotline.

Director of National Intelligence James Clapper said at a briefing on security threats Tuesday that he is "very concerned about the actions of the new young leader … and the rhetoric that has been emanating from the North Korean regime."

"The rhetoric, while it is propaganda-laced, is also an indicator of their attitude and perhaps their intent," he said. "So for my part I am very concerned about what they might do and they are certainly, if they so chose could initiate a provocative action against the South."

"There's perhaps nowhere else on earth where the capacity to wreak enormous damage is matched by the possibility of North Korea using their nuclear weapons," said Senate Intelligence Committee chairwoman Sen. Dianne Feinstein (D., Calif.) during the annual threat briefing.