CNN said Tuesday that U.S. spy satellites have detected new activity at North Korea's underground nuclear test site for the first time in several weeks.
 
Citing U.S. officials the report said the activity appears to involve some modifications around one of the tunnel entrances to an underground test area.
 
The officials told CNN that it's not yet clear if the activity indicates that a sixth nuclear test is imminent but they noted there's concern that North Korea could conduct a test during Wednesday's visit to Washington by top Chinese diplomats and military officials.
 
CNN said that Washington officials have known that the site is ready to conduct an underground test for some time.

[Photo : ]