The U.S. and Iran will resume indirect talks on reviving the 2015 nuclear deal in Vienna on Thursday, a U.S. official told Axios.

Why it matters: U.S. officials are concerned the nuclear deal is close to becoming irrelevant, as Iran has taken steps to advance its nuclear program and limit the work of UN inspectors.

• "We are headed back to Vienna with low expectations but are going to make a good faith effort," the U.S. official said.

The big picture: EU foreign policy chief Josep Borrell recently presented a new and updated draft agreement and called on Iran to make a decision on the proposal.

• Borrell wrote in a Financial Times op-ed last week that after 15 months of negotiations, he has concluded that “the space for additional significant compromises has been exhausted."
• But Borrell added that his draft agreement "represents the best possible deal … decisions need to be taken now … if the deal is rejected, we risk a dangerous nuclear crisis."

What they're saying: EU political director Enrique Mora, who is the coordinator of the talks, tweeted on Wednesday that he was on his way to Vienna and that the talks will focus on the draft the EU has proposed. 

• The U.S. official told Axios that Thursday's talks won’t be a new round of negotiations but an attempt to see whether it was possible to do the “fine-tuning” needed to reach an agreement on the basis of the draft.
• “If Borrell thinks this is necessary to see that we haven’t left any stone unturned, we appreciate it and are ready to do it but we are entering this with our eyes wide open," the U.S. official said.
• The official added that everyone knows what the agreement needs to look like and stressed that, to get a deal, Iran needs to lift its demands about issues that are outside the 2015 nuclear agreement.
• The U.S. official stressed that while Iran is advancing its nuclear program during the negotiations, the U.S. is not sitting idly by and is continuing to put more pressure on Iran by imposing additional sanctions.

State of play: The most recent round of indirect talks between the U.S. and Iran a month ago in Qatar ended with no progress and no date set for another round.

• During his trip to the Middle East, President Biden said the U.S. wouldn't "wait forever" for Iran to respond to its proposal to revive the deal.

Go deeper: Biden adviser says return to Iran deal "highly unlikely" in near future

Editor's note: This story has been updated with additional details throughout.