Seoul, South Korea ? South Korean and U.S. officials are trying to confirm whether recent movements at North Korea’s suspected nuclear testing site indicate the communist regime is planning another test explosion, news reports said Saturday.

Seoul is keeping a close watch on the movement of trucks and soldiers at the Punggye-ri site in North Korea’s remote northeast, Yonhap news agency reported, citing several unidentified military officials. One official, however, said a second test was “not believed to be imminent.”

“We are closely monitoring to see if these are preparations for a second nuclear test,” another official was quoted as saying.

South Korea also has detected a new building being erected at the site, the JoongAng Ilbo newspaper reported, citing unidentified officials.

Separate U.S. and South Korean studies have detected abnormal radiation in air samples, confirming the North conducted a nuclear test blast. The South Korean government has pointed to Punggye-ri as the most likely site of an underground test blast.

South Korea’s Defense Ministry said it could not confirm the reports. The U.S. State Department refused to comment.