U.S. officials have expressed sharp pessimism about the possibility of restoring the nuclear deal with Iran, days before the appointment of President-elect Ibrahim Raisi.

"There is a real danger that they will come back with unrealistic demands as to what they can achieve in these talks," said Robert Mali, the United States' chief subject and giver.

According to the New York Times, the concerns came after U.S. negotiators believed the previous Iranian government was on the verge of reaching an agreement before Raisey, a tough cleric and head of the country's justice system, came to power.

The US fears that the new government in Iran will accelerate the uranium enrichment process and increase the acquisition of technical knowledge, given the lack of international inspectors to maintain nuclear facilities, which could lead to further Iranian demands in negotiations.

The American newspaper says both sides will lose a lot if no agreement is reached, as President Biden's ultimate goal is to rehabilitate the agreement signed in 2015 under former President Barack Obama.

While negotiations stall, the US administration faces another dilemma represented by the inability of international inspectors to access Iran's nuclear energy facilities, which has recently increased its ability to produce nuclear fuel.

The inspection teams were denied entry to many of the facilities they regularly visited, measuring enrichment levels and calculating every gram of materials produced, as well as closing surveillance cameras and sensors last June.