Iran will enrich uranium with thousands of advanced centrifuges at two nuclear facilities, U.N. atomic energy agency says, further raising tensions.

Iran announced Friday it was activating new advanced centrifuges – which enrich uranium for the country’s nuclear program – after the United Nations’ nuclear watchdog criticized the country for not cooperating with the agency.

A rebuke of Iran led by the U.S. and its close allies at the global nuclear watchdog agency has drawn a vow by the Islamic republic to further ramp up uranium enrichment.