Threats from the Iran-backed Houthi militant group this week to block Saudi Arabia’s use of the Red Sea risk cutting off a crucial alternative path for Mideast oil and further destabilizing a global energy market upended by the war in Iran.

Since March, the Saudis have been moving millions of barrels of oil west each day through a pipeline and loading it onto tankers. From there, most of the vessels have navigated the Bab al-Mandab strait, a waterway at the southern end of the Red Sea, mostly to customers in Asia.

Before the war, one-fifth of the world’s oil passed through the Strait of Hormuz. Now, another choke point might be turned into a geopolitical weapon, underlining how drastically trade routes have been scrambled. Energy producers that devised workarounds to deliver shipments are now facing the possibility of needing to map new routes.

It was not apparent how or even whether the Houthis, who are based in Yemen, will carry through on their declaration, which they issued on Monday. But there were signs that the threat could be affecting sea traffic. Two oil tankers heading toward the Bab al-Mandab made U-turns and were moving north toward the Suez Canal, according to Kpler, a maritime data company. But that route can be costlier and logistically more complex.

On Tuesday, more than 93 crude oil tankers were operating in the Red Sea, a big increase from the approximately 50 tankers a day before the war, Kpler found, a reflection of the increased use of Saudi Arabia’s Yanbu port on the Red Sea. In recent months, Saudi Arabia has been exporting around 3.6 million barrels of oil and related fuels a day via the Bab al-Mandab strait. Before the war, the Saudis exported fewer than one million barrels per day via that route. Most of the oil shipped from Saudi ports south through the Red Sea is sent to South Korea, Japan, China and other destinations in Asia.

Even though the redirection of oil flows away from the Persian Gulf has allowed Saudi Arabia to continue delivering energy supplies to global markets, its overall exports of crude are running at a fraction of prewar levels.

According to a shipping executive, speaking on the condition of anonymity over concerns about the safety of his seafarers and vessels, shipowners received an email dated Monday from the Houthis warning them against loading cargo at Saudi Arabian ports. A Houthi official confirmed the email.

Oil traders have so far not reacted strongly to the Houthi threat. Brent, the global oil benchmark, is up about 3 percent this week to above $90 a barrel.

Several factors are cushioning oil prices. China is importing much less oil, and the United Arab Emirates is producing more, Ian Bremmer, the president of Eurasia Group, a geopolitical risk consultancy, wrote in a note. At the same time, the United States still has enough stockpiles of gasoline and diesel to meet roughly two months’ worth of demand.

But any attack on ships or infrastructure in the Red Sea would have a chilling effect on the market, analysts said.

“Even if one tanker gets hit by a drone, then that very much sends a signal to shipowners and crews,” said Hamad Hussain, an economist with Capital Economics, a consulting firm. “It would only take a couple to spook ships from making the trip.”

If Saudi Arabia deems shipping oil via the Red Sea’s Bab al-Mandab strait too risky, it has alternatives: It could send oil and fuels north to the Mediterranean via a pipeline in Egypt or the Suez Canal.

That approach, however, would be logistically challenging, not to mention very expensive. The Egyptian pipeline cannot accommodate all the oil that Saudi Arabia is currently sending south, and the Suez Canal is too shallow for fully loaded crude tankers. It would take an extra four weeks to export oil from Saudi Arabia to Asia via the northern route, said Matt Smith, a Kpler analyst.

The Houthis have caused lasting disruptions in the Red Sea in the past, attacking ships in 2023 shortly after the onset of the Gaza war. Today, Red Sea traffic is at only 55 percent to 60 percent of what it was before 2023, according to data from Windward, a maritime data firm.

The latest threats come at a particularly difficult time, with Iran’s attacks on ships transiting the Strait of Hormuz prompting many shipowners and operators to decide it is too dangerous to use that waterway. The strait has been practically at a standstill, with the exception of a brief cease-fire, since the United States and Israel launched strikes on Iran on Feb. 28. Only 12 ships passed through the critical waterway on Monday, Kpler said, down from about 130 before the war.

The Houthis control a significant part of Yemen. The threat to blockade Saudi Arabia, a U.S. ally, risks opening a new front in the regional war and further disrupting global energy supplies. Last week, the Houthis accused Saudi Arabia of striking Yemen’s main international airport in Sanaa.

But Gregory Brew, a senior analyst with the Eurasia Group, said the last time hostilities flared between Saudi Arabia and Yemen in 2023, the Houthis appeared to avoid attacking ships carrying Saudi oil.

That history, he said, has given investors some hope that the newest Houthi threats will not escalate. And yet even a limited offensive by the Houthis would worry markets and raise prices, Mr. Brew said. If that happens, he said, “Oil prices would be likely to climb above $100 a barrel this month unless we get decisive de-escalation between the United States and Iran.”

Shuaib Almosawa contributed reporting from Sanaa, Yemen.

The Iran-backed Houthi militia in Yemen on Monday said it would impose a maritime blockade on Saudi Arabia, a U.S. ally, in a move that threatened to open a new front in the regional war and further disrupt global energy supplies.

The Houthis did not offer any specifics on what such a blockade would entail. But the territory controlled by the Houthis in Yemen sits alongside the Bab al-Mandab, a narrow waterway that leads into the southern end of the Red Sea.

Yahya Saree, a Houthi military spokesman, said in a televised address on Monday that the move came in response to what he called a “continued Saudi siege” on Yemen, accusing the neighboring country of keeping ports and airports closed and imposing land, sea, and air restrictions for years.

Mr. Saree said Houthi forces were ready to respond to any Saudi reprisal, warning that any move by Riyadh would be met with “a total and harsh escalation.” The Saudi government and a Saudi-led military coalition did not respond to requests for comment.

During the Israel-Hamas war in Gaza that began in late 2023, the Houthis menaced ships in the Red Sea, hijacking them and attacking with drones and missiles. Their bombardment forced shipping companies to divert their cargo around the Cape of Good Hope, at Africa’s southern tip, sending global shipping costs soaring.

An escalation by the Houthis would only deepen regional chaos after a U.S.-Iran truce unraveled over the past few weeks, with the two sides and their respective regional allies reverting to daily attacks on each other. In the war, which began at the end of February when the United States and Israel assailed Iran, Iran has retaliated widely against U.S. allies including Jordan and Persian Gulf states like Saudi Arabia.

Dueling Iranian and American blockades of the Strait of Hormuz, another critical waterway, have upended global oil markets throughout the war, creating volatility and raising the price of energy supplies.

The Houthis — an armed faction that is part of the so-called “axis of resistance” led by Iran — have been fighting Yemen’s internationally recognized and Saudi-backed government since they overran the Yemeni capital, Sana, in 2014.

Last week, a four-year truce between Saudi Arabia and the Houthis in Yemen crumbled after the group accused Saudi Arabia of bombing Yemen’s main international airport in an attempt to prevent an Iranian plane from landing in Sana. After the bombing, the Houthis fired ballistic missiles toward an airport in southern Saudi Arabia.

Analysts say the past week’s developments are connected to the broader regional war.

“That’s a narrative that plays well with their audience inside Yemen. But in reality, it’s closely tied to Iran,” said Ahmed Nagi, a senior Yemen analyst at the International Crisis Group. “If this confrontation expands to affect the Bab al-Mandab, the consequences would go far beyond Saudi. It would have a major impact on global trade.”

A Houthi maritime blockade on Saudi Arabia in the Red Sea could affect more than 3 percent of the global oil market. Saudi Arabia has leaned on the Bab al-Mandab in recent months to export more than 3.6 million barrels of oil and related fuels a day, most of it to Asia, according to the maritime data firm Kpler.

Yasir al-Rumayyan, the chairman of Saudi Arabia’s state oil giant, recently said the ability to bypass the blocked Strait of Hormuz and use those Red Sea export terminals had been a “lifeline” for the kingdom’s economy.

Lisa Friedman and Rebecca F. Elliott contributed reporting.