The US State Department on Monday urged North Korea to refrain from escalating tensions after indications emerged of the communist nation resuming operations at its plutonium-producing nuclear reactor.

The North Korea-monitoring website 38 North has reported that recent satellite imagery showed the North restarting the 5-megawatt reactor at its Yongbyon nuclear complex after completing reprocessing spent fuel unloaded from the reactor.

The State Department declined to confirm the report, but urged restraint.

"We are not going to comment on matters of intelligence. We continue to call on North Korea to refrain from actions and rhetoric that further raise tensions in the region and focus instead on taking concrete steps toward fulfilling its international commitments," Katina Adams, a State Department spokeswoman, told Yonhap News Agency.