North Korea could conduct its seventh nuclear test as early as this month, the U.S. State Department said on Friday.

The assessment comes after satellite imagery analysis has revealed ongoing movement and activity at North Korea’s Punggye-ri test site for months consistent with restoration work on tunnels leading to the underground nuclear test facility.

“The United States assesses that the DPRK is preparing its Punggye-ri test site and could be ready to conduct a test there as early as this month, which would be its seventh test,” said State Department principal deputy spokesperson