The president of the Korea Economic Institute in Washington says a new building was being built at the Yongbyon nuclear site in North Korea when he visited the North last week.

Jack Pritchard met with South Korea's top nuclear envoy Wi Sung-lac on Wednesday to discuss the results of his trip to the North.

A diplomatic source in Seoul cited Pritchard as saying that during his visit, he saw construction work being done on a new building at Yongbyon. The source said Pritchard was unsure about whether the new building was a nuclear facility.

The source says Pyongyang officials told Pritchard that a five-megawatt reactor in Yongbyon was not operational.

The North also reportedly told Pritchard that it is willing to wait if South Korea, the U.S. and Japan are not ready to resume the stalled six-party nuclear talks.