Oil prices fell slightly on Monday ahead of the unveiling by U.S. Treasury Secretary Scott Bessent of the toughest set of Iran sanctions yet. File Photo by Yuri Gripas/UPI | License Photo

Aug. 24 (UPI) -- Oil prices fell slightly on Monday ahead of the unveiling by U.S. Treasury Secretary Scott Bessent of the toughest set of Iran sanctions yet.

The futures contract for Brent crude, the international benchmark, fell by around 1.4% to $93.09 a barrel while the contract for West Texas Intermediate, the American benchmark, retreated by a little over 1.6% to $85.65 a barrel as investors waited to find out what was in the package.

"At dawn begins an economic D-Day -- the single greatest financial offensive ever marshaled against an adversary," Bessent said in an online post late Sunday.

Separately, Bessent said in an op-ed piece that war with Iran was "entering the endgame" and criticized countries that purchase and ship Iranian oil in defiance of sanctions, avoiding mentioning China by name with President Donald Trump set to host President Xi Jinping in the White House in just over four weeks' time.