WASHINGTON : Donald Trump said on Wednesday he ordered an investigation into major oil companies over high gasoline prices as the US leader faces criticism over the impact of the Mideast war.

Global petroleum prices soared after Iran blocked the flow of oil through the vital Strait of Hormuz in response to US-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.

Gasoline prices are a political issue in the United States, where fossil fuel-powered vehicles are many Americans primary means of transport.

Trump has faced criticism for launching the war and its impact on the fuel costs paid be millions of Americans as November's congressional elections draw closer.

The president repeatedly predicted that fuel prices would "come down like a rock" after the conflict ended.

But economists dispute that claim, expecting oil prices to take months to return to pre-war levels.

Tehran and Washington have struck an initial deal that includes the resumption of oil tanker traffic through Hormuz, though issues like Iran's nuclear programme are still in dispute.

Gasoline prices are still above their pre-war levels, but have come down since the initial deal was announced.

The average price of a gallon (3.8 litres) of regular gasoline logged in at $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 skyrocket in the United States.