Tehran also said it would not accept “artificial” solutions to U.S. sanctions.

Iran is threatening to exceed the maximum amount of enriched uranium allowed it by the deal, in retaliation for crippling U.S. economic sanctions imposed in the past year.

It is just days away from that limit, according to diplomats, and going over it could unravel the accord.

Senior officials from Iran and the deal’s remaining parties will meet with the aim of saving the pact. But with European powers limited in their ability to shield Iran’s economy from U.S. sanctions, it is unclear what they can do to provide the large economic windfall Tehran wants.

On Friday, Iran’s Fars news agency quoted foreign ministry spokesman Abbas Mousavi as saying, “I think this meeting can be the last chance for the remaining parties to gather and see how they can meet their commitments towards Iran.”