U.S. President Donald Trump has caused uncertainty on whether a deal with Iran to end the war will be reached, only a day after saying such an agreement was imminent.

Trump, in a statement posted to Truth Social, stressed a deal that is reached would be a “good and proper one.”

“If I make a deal with Iran, it will be a good and proper one, not like the one made by [President Barack] Obama, which gave Iran massive amounts of CASH, and a clear and open path to a Nuclear Weapon,” Trump wrote.

He went on to say their deal — which he added “nobody has seen it, or knows what it is” — would be the “exact opposite” of the deal reached in 2015.

That deal lifted most U.S. and international economic sanctions against Iran. In exchange, Iran agreed to restrictions on its nuclear program, making it impossible to produce a bomb and establishing rigorous inspections.

Three years after the deal was reached, Trump announced the U.S. was withdrawing.

While Trump keeps stressing a deal would prevent nuclear weapon development, Iran has not publicly committed to giving up its enriched uranium.

“Both sides must take their time and get it right. There can be no mistakes,” Trump wrote. “They must understand, however, that they cannot develop or procure a Nuclear Weapon or Bomb.”

Uranium enrichment and possession would be a part of the potential deal that Trump previously noted in his Saturday post, according to Secretary of State Marco Rubio.

During a visit to India, Rubio said there had been “significant progress, although not final progress” in negotiations with Iran with bans and restrictions surrounding nuclear proliferation.

“Iran needs to enter into serious negotiations on three topics: their pledge never to have nuclear weapons, restrictions long-term on their enrichment capabilities, and what do you do with the highly-enriched uranium,” Rubio told India Today.

Iran appeared to respond to Rubio’s comments, with its embassy in India posting on social media that it has an “inalienable” right to nuclear technology.

Were a deal to be reached, it’s anticipated the Strait of Hormuz would also reopen, easing a worldwide energy crisis that was sparked by the U.S. and Israel’s bombardment of Iran that started Feb. 28. In response. Iran effectively closed the key waterway, leading to price spikes for oil, gas and several related products.

The U.S. has also enacted its own measures, blockading Iranian ports for more than a month. Trump said on Sunday the blockade would “remain in full force and effect until an agreement is reached, certified, and signed.”

—with files from The Associated Press