The United States’ President, Donald Trump has directed the Department of Justice to investigate major oil companies over allegations that they have failed to reduce petrol prices in line with falling global crude oil prices.

Trump announced the directive in a social media post, accusing energy firms of charging motorists more than necessary despite paying less for crude oil. He said petrol prices at filling stations had not declined at the pace he expected.

“The big oil companies are not dropping their price at the pump commensurate with the sharply lower prices they are paying for oil,” Trump said, alleging that consumers were being overcharged.

The president did not identify any company in his post, but said the Justice Department should begin looking into the matter immediately.

His comments come as international oil prices continue to ease following sharp increases linked to the conflict involving Iran, the United States and Israel.

Oil markets became volatile after the US and Israel launched attacks on Iran on February 28. Iran later disrupted movement through the Strait of Hormuz, a key global shipping route for crude oil and gas, leading to supply concerns and a spike in energy prices.

Brent crude, the international benchmark, climbed to nearly $120 per barrel in May at the height of the market disruption. It has since declined to about $76 per barrel as peace negotiations advance, although it remains above the roughly $70 per barrel level recorded before the conflict.

In the United States, the average retail price of regular petrol has dropped to around $3.90 per gallon after rising above $4 in April. However, prices remain higher than they were before the war.

The Department of Justice and the White House had not immediately responded to requests for comment.