"EVERYONE, KEEP OIL PRICES DOWN. I'M WATCHING!" Trump wrote on his Truth Social platform minutes after Wall Street started trading, with major US indexes treading water.

Trump cautioned against "playing right into the hands of the enemy."

Iran has vowed to retaliate after US air strikes on its nuclear facilities, and its options include closing the strategic Strait of Hormuz.

Disrupting traffic through the vital route for oil and gas -- which carries one-fifth of global oil output -- would send energy prices soaring in a global inflationary shock.

Trump urged the US Energy Department in a separate social media post to "DRILL, BABY, DRILL!!! And I mean NOW!!!"

Iran is the ninth-biggest oil-producing country globally and exports just under half of the 3.3 million barrels it produces each day.

International benchmark crude contract Brent and US equivalent WTI both rocketed more than four percent to their highest price since January when trading opened on Monday.

They later slipped briefly into the red and edged up 0.3 percent as Wall Street opened for trading.

For now, it does not appear that the oil market expects Iran would close off the Strait of Hormuz, even as traders nervously await the next move.