Iran has remained within the main limits on its nuclear activity set by its 2015 deal with six world powers, the U.N. atomic watchdog said in its first report since U.S. President Donald Trump decertified Iranian compliance with the terms.

Iran undertook to curb its uranium enrichment program in return for relief from international sanctions that crippled its economy, and U.N. nuclear inspectors have repeatedly verified Tehran’s adherence to the key aspects of the accord.

Trump has called the agreement between Iran, the United States, Britain, France, Germany, Russia, China and the European Union “the worst deal ever” and he disavowed Iran’s compliance last month. His decision did not constitute a U.S. exit from the accord but raised concern about its staying power.

Trump’s move, at odds with the commitment of the other parties to the deal, meant the U.S. Congress must decide by mid-December whether to reimpose economic sanctions lifted under the accord, reached under his predecessor Barack Obama.

If Congress reimposes the sanctions, the United States would in effect be in violation of the deal and it would likely fall apart. If lawmakers do nothing, the deal remains in place.

In response, Iranian Supreme Leader Ayatollah Ali Khamenei has said Tehran will stick to the nuclear accord as long as the other signatories respected it, but would “shred” the deal if Washington pulled out.

If the deal unravels, it would strengthen hardline opponents of Hassan Rouhani, Iran’s pragmatist president who opened up diplomatic channels to Western powers to enable nuclear diplomacy after years of worsening confrontation.