Amid suspicions that North Korea resumed operations at its main plutonium-producing reactor, Washington has urged Pyongyang to refrain from raising tensions on the Korean Peninsula.

In an interview on Monday with Seoul-based Yonhap News Agency, State Department Spokeswoman Katina Adams said the U.S. continues to call on North Korea to focus on taking concrete steps toward fulfilling its international commitment.

She, however, declined to verify the authenticity of a recent report by "38 North," saying that the U.S. government does not comment on intelligence-related matters.

Researchers at the North-tracking Web site claimed last Friday a water plume was coming from the cooling water outlet of the reactor at the North’s Yongbyon nuclear site, calling it an indication that the reactor is “very likely operating.” 

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