U.S. President Donald Trump said early Wednesday that he had ordered the Justice Department to investigate oil companies over high gasoline prices.
Global petroleum prices surged after Iran blocked the flow of oil through the vital Strait of Hormuz in response to U.S.-Israeli strikes in February.
"The big Oil Companies are not dropping their price at the pump commensurate with the sharply lower prices they are paying for Oil," Trump wrote on Truth Social.
"Those prices are dropping like a rock! In other words, customers are being 'gouged,'" he added.
"I have instructed the DOJ to immediately start looking into this. Gasoline prices better start going down a lot faster than what I'm seeing!" Trump said.
On Tuesday, Trump said the average national gasoline price was down 60 cents a gallon "just from a short while ago."
Gasoline prices are a political issue in the United States, where fossil fuel-powered vehicles are the primary means of transportation for many Americans.
Trump has faced criticism for launching the war and for its impact on fuel costs paid by millions of Americans as November's congressional elections draw closer.
The president has repeatedly predicted that fuel prices would "come down like a rock" after the conflict ended.
However, economists dispute that claim and expect oil prices to take months to return to prewar levels.
Tehran and Washington have reached an initial deal that includes the resumption of oil tanker traffic through the Strait of Hormuz, though issues such as Iran's nuclear program remain unresolved.
Gasoline prices remain above prewar levels but have declined since the initial deal was announced.
The average price of a gallon, or 3.8 liters, of regular gasoline was $3.93 on Tuesday, according to the AAA motor club.
Trump has faced backlash from Americans who accuse him of pouring billions of taxpayer dollars into the Middle East war while oil prices and inflation rise in the United States.
Last week, the average U.S. gasoline price dropped below $4 per gallon for the first time since March after the U.S. and Iran announced a memorandum of understanding to end their conflict and restore shipping through the Strait of Hormuz.