Oil prices retreated on Monday ahead of an expected announcement of new measures by the United States aimed at further isolating Iran economically.

Treasury Secretary Steven Mnuchin said he will detail what President Donald Trump has called an "economic D-Day" for Iran on Monday afternoon in Washington.

In an opinion essay in The Financial Times, Mr. Mnuchin said the six-month war with Iran was "entering the endgame."

Without specifying what measures might be taken, Mr. Mnuchin took aim at countries that "enable and purchase and transport its petroleum," seemingly pointing the finger at China, which has been the main buyer of Iranian crude in recent years. Iran has warned it would strike the interests of neighboring states if they joined the U.S. efforts.

Oil prices slide. Shipping disruption in the Gulf grinds on. Bonds yields ease. Stocks slip. Gasoline prices edge higher.