Two oil tankers near the strategic Strait of Hormuz have been damaged in suspected attacks, an assault that left one ablaze and adrift as sailors were evacuated from both vessels.
The US Navy rushed to assist amid heightened tensions between Washington and Tehran.
The Navy and the ship's owners offered no immediate explanation on what weapon caused the damage to the MT Front Altair and the Kokuka Courageous in the Gulf of Oman off the coast of Iran, though all believed the ships had been targeted in an attack.
Benchmark Brent crude spiked at one point by as much 4 per cent in trading following the suspected attack, to over $62 a barrel, highlighting how crucial the area remains to global energy supplies. A third of all oil traded by sea passes through the strait, which is the narrow mouth of the Persian Gulf.
Cmdr. Joshua Frey, a 5th Fleet spokesman, said the US Navy was assisting the two vessels that he described as being hit in a "reported attack." He did not say how the ships were attacked or who was suspected of being behind the assault.
The firm that operates the Front Altair told The Associated Press that an explosion was the cause of the fire onboard. International Tanker Management declined to comment further saying they are still investigating what caused the explosion. Its crew of 23 is safe after being evacuated by the nearby Hyundai Dubai vessel, it said.
The second vessel was identified as the Kokuka Courageous. BSM Ship Management said it sustained hull damage and 21 sailors had been evacuated, with one suffering minor injuries.
Iranian state television said 44 sailors from the two tankers have been transferred to an Iranian port in the southern province of Hormozgan.
Tensions have escalated in the Mideast as Iran appears poised to break the 2015 nuclear deal with world powers, an accord that the Trump administration pulled out of last year.
Iran's nuclear deal, reached in 2015 by China, Russia, France, Germany, the United Kingdom and the US, saw Tehran agree to limit its enrichment of uranium in exchange for the lifting of crippling sanctions.
Western powers feared Iran's atomic program could allow it to build nuclear weapons, although Iran long has insisted its program was for peaceful purposes.
Iran says it quadrupled its production of low-enriched uranium.
Meanwhile, US sanctions have cut off opportunities for Iran to trade its excess uranium and heavy water abroad, putting Tehran on course to violate terms of the nuclear deal regardless.