U.S. spy satellites detect activity at North Korean nuclear test site

U.S. spy satellites have detected new activity at North Korea's underground nuclear test site for the first time in several weeks.

The activity appears to involve some modifications around one of the tunnel entrances to an underground test area, the CNN quoted two U.S. officials as saying.

The officials said it is not yet clear if the activity indicates a sixth nuclear test is imminent, but noted there is concern that North Korea could set off a test during Wednesday's visit to Washington by top Chinese diplomats and military officials.

They also said that military options for North Korea have recently been updated, and will be presented to President Donald Trump for a decision to act if there is a nuclear test.