President Donald Trump ordered a naval blockade of the Strait of Hormuz on Sunday, dimming hopes for a quick end to the conflict in the Middle East and escalating a standoff with Iran that has already triggered the worst energy shock in history.

The blockade would take effect at 10 a.m. ET Monday, targeting vessels of all nations entering or departing Iranian ports and coastal areas, including those on the Arabian Gulf and Gulf of Oman, the U.S. Central Command said in a statement.

Tanker traffic through the strait, which had begun to inch higher after a two-week ceasefire announced by Trump last week, came to a halt again within hours of Trump’s announcement, according to Lloyd’s List Intelligence. At least two vessels that had appeared to be heading for the exit turned back.

Crude oil surged as investors scrambled to price in a further squeeze on Persian Gulf supply. U.S. WTI futures for May delivery jumped more than 8% to $104.40 a barrel, while Brent crude rose over 7% to $101.86.

Trump’s order came after 21 hours of weekend negotiations between Washington and Tehran collapsed without an agreement on Iran’s nuclear program, control of the waterway, and Israel’s continued attacks against the Iranian-backed Hezbollah in Lebanon.

Before the opening strikes by the U.S. and Israel against Iran on Feb. 28, roughly one-fifth of the world’s oil passed through the Strait of Hormuz. That flow has since slowed to a trickle, upending supply chains for oil, fertilizers, apparel and industrial goods. Analysts have warned that clearing the backlog could take weeks even after a resolution.

A full blockade would further tighten the squeeze. “Taking more oil off the market — particularly the only oil that is now getting out from the Persian Gulf — will drive oil prices further up … [to] around $150 per barrel,” Trita Parsi, executive vice president of the Quincy Institute for Responsible Statecraft, said on CNBC’s “The China Connection” on Monday.

Besides crude, commodity prices for fertilizer and helium — critical inputs for food production and semiconductor manufacturing — are likely to keep climbing, fanning inflation that is already accelerating, said Ben Emons, managing director at Fed Watch Advisors.

The IMF and World Bank officials last week signaled they would downgrade global growth forecasts and raise inflation projections, warning that emerging markets would be hit hardest.

“The economic scarring from attacks on energy facilities and ports in Iran and other Gulf nations could continue to keep supply under stress in emerging Asia,” Barclays said. “It remains to be seen how quickly the extraction, refining, and loading of oil and gas can be normalized.”

The month-long disruption in the Strait of Hormuz has sparked warnings of an energy shortage worse than the 1970s oil crisis, when an embargo by Arab producers on countries aligned with the U.S. quadrupled oil prices, prompting fuel rationing across major economies.

Fatih Birol, head of the International Energy Agency, last week called the disruption the worst energy shock the world has ever seen — more severe than the oil crises of the 1970s and the Ukraine war combined.

“This is a historic disruption to world oil,” Daniel Yergin, vice chairman of S&P Global, said in an interview with Barron’s last month. “There has never been anything of this scale. Even the oil crises of the 1970s, the Iran-Iraq war of the 1980s, Iraq’s invasion of Kuwait in 1990 — none of those come close to the magnitude of this disruption.”

Yet the price response has so far been more muted, and economic growth may prove more resilient than feared, said David Lubin, senior research fellow at Chatham House. He noted that the global economy is less oil-intensive than in the past, with oil use per unit of GDP now requiring roughly 40% of a barrel of oil, compared with a full barrel in the early 1970s. Wind, solar and nuclear have also diversified the energy mix in ways that didn’t exist five decades ago, Lubin noted.

Should the conflict escalate further, “it’s quite possible that the energy impact of this crisis could start to deliver as big a negative shock as the 1970s crisis did,” he said.

The blockade also risks drawing the world’s second-largest economy into the confrontation. China remains Iran’s largest oil buyer and has continued to receive shipments through the strait since the war began, analysts say.

A blanket ban on tankers carrying Iranian crude threatens to cut off that supply, potentially reigniting U.S. tensions with Beijing ahead of Trump’s planned trip to China next month. “I doubt Trump is ready for that escalation,” said Parsi, adding that “it wouldn’t be surprising” if Trump walks back on the earlier threats.

The Trump administration on Monday also threatened to impose an additional 50% tariff on China if Beijing supplies advanced defense equipment to Tehran.

Countries including India and Pakistan, which have negotiated safe-passage arrangements with Iran, could also find themselves caught in the crossfire, Parsi said.

Some analysts see the blockade as coercive leverage rather than a terminal escalation. “Since neither side has explicitly stated that talks won’t resume or that the ceasefire is over, all these moves should be treated as tactics and threats within the negotiations,” Parsi said.

Brian Jacobsen, chief economist at Annex Wealth Management, was cautiously optimistic, suggesting Washington may carve out safe-passage exemptions for allied vessels. But Emons warned that the strategy carries serious downside risk.

A move designed to bring Iran “to its knees” could just as easily trigger counterstrikes and a fresh cycle of military escalation, he said.

Iran’s Islamic Revolutionary Guard Corps signaled as much, warning on Sunday that any military vessels approaching the strait “under any pretext” would be considered a ceasefire violation. It also hardened its rhetoric, saying that enemies would be trapped in a “deadly vortex” in the case of any miscalculation.

The blockade is also legally contentious, according to several experts, as neither the U.S. nor Iran has the authority to close or impede passage through Hormuz.

“Under international law, specifically the rules governing international straits, the U.S. has no legal authority to close, suspend, or impede transit passage through Hormuz,” said Emons. Only Iran and Oman are coastal states, and even they are prohibited from suspending transit passage, he added.

For shipowners, the practical deterrent from traversing through the strait also includes exposure to Western sanctions on Iran. Payments to Iran risk breaching U.S. and European rules, and firms may face severe penalties, according to Lloyd’s List Intelligence.