Iran has discovered a new oilfield in the southwest of the country that has the potential to boost its reserves by about a third, President Hassan Rouhani said on Sunday, according to a Reuters report.

“Workers and the exploration arm of the National Iranian Oil Company …have found an oilfield with 53 billion barrels of reserves,” Rouhani said in a televised speech in the central city of Yazd.

The field stretches over 2,400 sq km (927 sq miles) in the oil-rich Khuzestan province, Rouhani said.

Iran ranks as the world’s fourth–largest reserve holder of oil, and the second-largest holder of gas reserves, according to the US Energy Information Administration (EIA).

Iran had an estimated 157 billion barrels of proved crude oil reserves in January 2018, the EIA website said.

Since withdrawing from Iran’s 2015 nuclear deal with world powers, the United States has reimposed sanctions to strangle its vital oil trade.