Washington DC - President Donald Trump on Wednesday temporarily waived a century-old shipping law to help ease energy costs that have surged since US-Israeli strikes on Iran plunged the Middle East into war.

Trump's move to issue a 60-day Jones Act waiver would lift a ban on foreign-flagged vessels transporting cargo between US ports over this period.

The 1920 law was aimed at promoting American shipbuilding, but critics argue that it hampers free trade and has raised costs for consumers.

Trump's latest move is "just another step to mitigate the short-term disruptions to the oil market as the US military continues meeting the objectives of Operation Epic Fury," said White House Press Secretary Karoline Leavitt in a statement.

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"This action will allow vital resources like oil, natural gas, fertilizer, and coal to flow freely to US ports for sixty days," she added.

She vowed that the Trump administration "remains committed to continuing to strengthen our critical supply chains."

According to AAA motor group data, US gasoline prices have risen more than 27% since the start of the war.

A barrel of oil again skyrocketed past $100 on Wednesday after Israel launched attacks on a Iranian gas field, with severe retaliations against energy infrastructure in the Persian Gulf expected.