SEOUL - A senior US envoy called Monday for a calm response to the Democratic People's Republic of Korea (DPRK)'s reported pursuit of a uranium enrichment program, adding the US government knew of it beforehand.

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"We've known about this for some time," Stephen Bosworth reportedly said in a meeting with Seoul's foreign minister Kim Sung-hwan, according to Yonhap News Agency. "It's a very unfortunate development, but it's not a crisis," he reportedly added.

The meeting came after The New York Times reported Pyongyang showed US nuclear scientist Siegfried Hecker, who recently traveled to the DPRK, a vast, new plant to enrich uranium with " hundreds and hundreds" of centrifuges installed.

While the newly disclosed nuclear facility in the DPRK poses a challenge, it does not mean the US policy toward Pyongyang is a "failure", the envoy told reporters after meeting Kim.

Bosworth also sat down with Wi Sung-lac, Seoul's top representative for Six-Party Talks over denuclearizing Pyongyang, to discuss disclosed centrifuges and the DPRK's apparent move to build light-water nuclear reactor.

He is scheduled to visit Tokyo and Beijing before returning home on Wednesday. Wi is also set to leave for Beijing to sit down with his Chinese counterpart Wu Dawei.