An existing waiver, which temporarily allowed foreign flagged vessels to transport cargo between US ports, was due to expire by May 17. The latest move brings this end date to mid-August.

"New data compiled since the initial waiver was issued revealed that significantly more supply was able to reach US ports faster," said Taylor Rogers, a White House spokeswoman.

"This extension will help ensure vital energy products, industrial materials, and agricultural necessities are maintained," she added in a statement.

She said Trump has issued a 90-day extension.

US-Israeli strikes on Iran from February 28 plunged the Middle East into war, and triggered Tehran's retaliation in effectively closing off the Strait of Hormuz.

This has caused an energy supply crunch as the waterway is a key route for oil and gas transportation, sending prices rocketing.

US gasoline prices have also surged, piling pressure on household budgets ahead of key midterm elections.

Under the 1920 Jones Act, which was aimed at promoting American shipbuilding, cargo moved by water between US ports has to be transported on vessels that are US-built, US-owned and registered under the US flag.

But in March, the Trump administration granted a 60-day waiver to temporarily lift this requirement as economic fallout from the war intensified.

Oil prices remain steep, even if they have come off recent highs.