Oil prices declined on Monday as investors awaited details of what Washington has described as its toughest-ever sanctions campaign against Iran, while Tehran dismissed the threat of increased economic pressure.

West Texas Intermediate futures, the U.S. benchmark, fell 1.62 per cent to $85.65 per barrel, while Brent crude, the international benchmark, dropped 1.38 per cent to $93.09 a barrel.

U.S. Treasury Secretary Scott Bessent is expected to announce a new package of sanctions targeting Iran later on Monday.

“At dawn begins an economic D-Day — the single greatest financial offensive ever marshaled against an adversary,” Bessent said in a post on X.

The announcement comes after President Donald Trump last week threatened to launch what he described as the “most crushing economic operation ever taken against any country” against Iran.

He also warned of severe financial penalties for countries that assist Tehran in circumventing sanctions, describing the campaign as “Economic Warfare and Isolation on an unprecedented scale.”

Iran has rejected the threats, with the Islamic Revolutionary Guard Corps saying Tehran has measures “to counter the adverse effects of the enemy’s war” and can “easily establish economic relations with countries,” according to Iranian state media.