By Paul Eckert
WASHINGTON (Reuters) - The United States scolded North Korea on Thursday over reports indicating the reclusive nation has restarted a plutonium-producing nuclear reactor, emphasizing that such a move would violate U.N. Security Council resolutions.
U.S. officials in Washington and traveling in Asia, however, stopped short of confirming reports by two U.S. think tanks that steam rising over North Korea's Yongbyon nuclear complex indicated a reactor that was moth balled in 2007 was back in operation.
"Suffice to say, if it was true, it would be a violation of the relevant U.N. Security Council resolutions and, of course, contrary to North Korea's commitments under its September 19, 2005, joint statement," said State Department deputy spokeswoman Marie Harf.
Harf, who like other U.S. officials refused to discuss intelligence on the matter, was referring to a 2005 agreement signed by North Korea, four neighbors and the United States in which Pyongyang pledged to scrap its nuclear program in exchange for economic and energy aid. That deal unraveled in 2008.
"If it turns out these reports are true ... it would be a very serious matter," Special Representative for North Korea Policy Glyn Davies told reporters in Tokyo on Thursday.
On Wednesday, the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies and the Institute for Science and International Security (ISIS) released reports saying a satellite image from August 31 showed white steam rising from a building in Yongbyon.
ISIS President David Albright said the move was in line with North Korea's announcement in April that it would bring Yongbyon's five-megawatt research reactor on line.
"We know they're producing steam, but we don't know if this is a test or if the reactor is up and running," he said.
LIGHT WATER REACTOR CONSTRUCTION
Albright, a physicist and former nuclear inspector, said that in conversations with North Korean technicians "they said they've kept it operationally on standby. They have staff. They maintain it."
He said he doubted that the Yongbyon five-megawatt reactor could produce 6 kg (13.2 lbs) of plutonium a year, as initially estimated. But at 27 years old and with a simple design "well tested" by Britain and France, it still functions, he said.
Albright said a bigger proliferation worry was a light water reactor under construction at the Yongbyon complex. The August 31 satellite imagery that revealed steam also showed that the nearby light water reactor "appears to be externally complete" while work was likely going on inside, ISIS said on its website.
"The LWR (light water reactor) is much more threatening in terms of plutonium production," Albright said in a telephone interview. He said it had five times the capacity of the old Yongbyon reactor, but would require at least a year before it could be operational.
The new revelations have prompted calls for a renewal of diplomacy on North Korea. Talks have been largely on hold for years under President Barack Obama's policy of "strategic patience" that insists on a show that North Korea is serious about its 2005 disarmament pledge before resuming formal talks.
"We're working with our Asian partners to help the North Koreans realize that they need to abide by their international commitments," Scot Marciel, principal deputy assistant secretary of state for East Asian and Pacific Affairs, said in a speech in Washington on challenges in the region.
Michael Green, a former White House Asia adviser who took part in nuclear talks with North Korea under President George W. Bush, said Pyongyang's uranium enrichment and other nuclear work were bigger concerns than the Yongbyon reactor.
He predicted North Korea would before long conduct another nuclear test to follow those in 2006, 2009 and last February.
"They'll time it for strategic reasons, but the timing will be when they're technically ready," said Green, senior vice president for Asia at the Center for Strategic and International Studies think tank.
(Reporting by Paul Eckert; Editing by Will Dunham)