In a further effort to try and tame surging prices, the US issued its second temporary waiver for the purchase of Russian oil. The latest measure, which is for oil that was loaded onto vessels before March 12, is broader than a directive earlier this month that only cleared India to boost its buying.

The near-halt to shipping through the narrow Strait of Hormuz between Iran and the Arabian Peninsula has choked off shipments of crude, natural gas and products such as diesel to global customers, driving up energy prices. Several ships have been attacked this week, adding to the odds that owners won’t pass Hormuz anytime soon. That has raised fears of an inflation crisis and is starting to hit some economies.

The International Energy Agency warned on Thursday that the supply disruption is the largest in the history of the global oil market, a day after its members agreed to a historic release of emergency reserves to try and cool prices. Jet fuel is trading north of $200 a barrel in Europe, underscoring the impact on refined products.

“This is the most important oil supply disruption event since the 1970s,” said Philip Jones-Lux, senior market analyst at Sparta Commodities, referring to previous Middle East supply shocks. The IEA release helps to keep prices from going to “stratospheric levels,” but probably only for a short period, he added.

Iran has started laying mines in the Strait of Hormuz, the New York Times reported, citing US officials, which will make shipping even more perilous for those considering passing through the waterway. Since the war began on Feb. 28, vessel traffic through the channel has slowed to a trickle.

The US Navy could start escorting tankers through the strait by the end of March, Energy Secretary Chris Wright said on CNBC. Earlier this week, he wrote in a now-deleted social media post that the Navy had successfully escorted a tanker through the channel, a claim later walked back by the White House.