WASHINGTON, United States (AFP) — President Donald Trump on Monday again extended a waiver that allows foreign ships to carry oil and other commodities between US ports, as the war on Iran continues to disrupt energy flows and elevate costs.

The 90-day extension of relief from the Jones Act — which requires cargo between US ports to move on US vessels — comes shortly before an earlier waiver was due to expire in mid-August.

But the scope covered is narrower this time, focusing more on the transport of energy, a White House official confirmed Monday.

“Today, the Trump Administration issued a 90-day extension to the Jones Act waiver to ensure our military and key industries maintain uninterrupted access to critical resources,” said White House spokesperson Taylor Rogers.

“Data shows the waiver has driven a significant increase in domestic deliveries of essential products such as gasoline, diesel and jet fuel,” she added.

The relief this time also calls for reviews on the availability of US vessels before determining if the waiver applies to individual voyages.

The Cato Institute’s Colin Grabow and Scott Lincicome estimate that more than 54 million barrels of energy products have moved between US ports on over 200 voyages since March, when an earlier waiver was introduced.

“The waiver has unleashed domestic commerce that the Jones Act previously prevented,” Grabow and Lincicome said.

“In most cases, these voyages took place on vessels with no connection to US adversaries like China and supplied American companies with American energy products that would’ve otherwise been imported at a much higher cost,” they added.

Oil prices have surged after US and Israeli strikes targeting Iran from late February sparked a war that has since engulfed the Middle East.