Iran's oil production has recovered to the level it was at in 2018, before the U.S. unilaterally withdrew from a nuclear deal and reimposed sanctions on the country, a top Iranian official reported Monday.

"Oil production has reached pre-sanctions figures, despite economic pressures," said Mohsen Khojastehmehr, CEO of the National Iranian Oil Company (NIOC), quoted by state news agency IRNA on Sunday.

Iran is currently engaged in negotiations to restore the 2015 nuclear deal that would grant it much-needed sanctions relief in return for major curbs on its nuclear program.

The U.S., under then President Donald Trump, unilaterally withdrew from the deal in 2018 and reimposed stringent sanctions, prompting Iran to begin rolling back on its commitments under the deal the following year.

Production has been restored to the pre-sanctions level of 3.8 million barrels per day (bpd), Khojastehmehr said, after it had sharply declined following the reimposition of sanctions.

President Ebrahim Raisi's government invested $500 million to restore facilities and increase production to pre-sanctions levels within six months, he added.

Oil Minister Javad Owji said Friday that oil revenues for the last Iranian calendar year, which came to a close on March 20, registered $18 billion, about 2.5 times more than the previous year.

In a monthly report, the OPEC group of oil-producing countries estimated that Iran produced 2.54 million bpd of oil in February.