North Korea lashed out at the U.S. and the U.N. nuclear watchdog over their push for Pyongyang’s denuclearization on Monday, insisting its nuclear status is “irreversible” after the International Atomic Energy Agency (IAEA) raised concerns about continuing enrichment activity.

In a press statement carried by the Korean Central News Agency (KCNA), the DPRK mission in Vienna accused Washington of a “grave political provocation” for calling its nuclear access “illegal” and repeating its “anachronistic denuclearization assertion.”