US President Donald Trump has said the US navy will protect ships in the Middle East and the government will provide insurance "if necessary" in a bid to contain soaring energy prices sparked by the US-Israel war with Iran.

About 20% of the world's oil and gas flows through the Strait of Hormuz, a narrow waterway wedged between Iran and Oman. Traffic has almost entirely halted following Iran's threats to "set fire" to ships.

Trump has said the US government will provide risk insurance "at a very reasonable price" to all shipping firms in the region.

Experts warned these assurances might not be enough to ease companies' concerns.

“Effective IMMEDIATELY, I have ordered the United States Development Finance

Corporation (DFC) to provide, at a very reasonable price, political risk insurance and guarantees for the Financial Security of ALL Maritime Trade, especially Energy, traveling through the Gulf,” Trump wrote in a social media post.

“If necessary, the United States Navy will begin escorting tankers through the Strait of Hormuz, as soon as possible,” he wrote.

“No matter what, the United States will ensure the FREE FLOW of ENERGY to the WORLD.”

More than 150 ships are reported to have been stranded in the Strait of Hormuz.