U.S. President Donald Trump said on Wednesday that U.S. sanctions on Iran will be “increased substantially” in response to the regime last week exceeding the uranium-enrichment limit under the 2015 nuclear deal.

“Iran has long been secretly ‘enriching,’ in total violation of the terrible 150 Billion Dollar deal made by John Kerry and the Obama Administration,” tweeted Trump. “Remember, that deal was to expire in a short number of years. Sanctions will soon be increased, substantially!”

The United States withdrew from the deal in May 2018 and reimposed sanctions lifted under it, in addition to enacting new sanctions against Tehran.

On Wednesday, a special meeting about Iran’s nuclear program, reported by the International Atomic Energy Agency, was convened in Vienna as requested by the United States.

The U.S. ambassador to international organizations in Vienna, Jackie Wolcott, said at the meeting that the Iranian move was “nuclear extortion,” and that Tehran’s “misbehavior” and should “not be rewarded.”

She echoed that the Trump administration is “open to negotiation without preconditions.”