CAIRO — A large ship filled with explosive materials sitting incapacitated for years in the water. Experts repeatedly sounding alarms, warning of a major but preventable catastrophe. Yet the warnings were ignored.

This sounds like the run-up to Beirut’s deadly port explosion this week and Lebanon’s worst disaster in decades. Except that this scenario is unfolding off the western coast of Yemen, threatening to trigger the world’s worst-ever oil spill and untold ecological damage.

The destruction and deaths in Beirut have touched off concerns about a similar calamity happening in Yemen, with potentially devastating consequences for the Arab world’s poorest country, which is enmeshed in a civil war and a severe humanitarian crisis.

Since 2015, when Yemen’s conflict intensified, the FSO Safer oil tanker has been stranded in the Red Sea, rusting away with roughly 1.1 million barrels of oil on board. Its condition, says the United Nations, is deteriorating daily, increasing the chances of an oil spill if any of its tanks rupture. Seawater is already seeping into the vessel, according to U.N. reports.

If disaster strikes, the Yemeni tanker could release four times the amount of crude spilled in the Exxon Valdez disaster of 1989. That would harm marine life, disrupt vital Red Sea shipping lanes and shatter regional economies.

The Safer is also a potential bomb. Like the large stockpiles of explosive ammonium nitrate brought by a Russian ship into Beirut and later housed in a warehouse in its port, the oil stored in the tanker for years, without ventilation, poses a significant threat of explosion, say experts.

“The warnings about the ammonium nitrate in Beirut remained abstract to people,” said Ian Ralby, the chief executive of I.R. Consilium, a maritime security consulting firm, which has written extensively about the Safer. “They had no sense of what that sort of explosion would look or feel like, and they did not grasp the tremendous consequences of inaction and complacency.

“That is very similar to what has been happening with the FSO Safer.”

On Thursday, Yemen’s information minister, Moammar al-Eryani, warned of a “human, economic and environmental catastrophe” if the Safer sinks or explodes.

“The huge explosion at the Port of Beirut and its aftermath of heavy human casualties and catastrophic damage to the Lebanese economy and environment remind us of the ticking bomb Safer,” Eryani told the Yemeni news agency Saba.

For years, the United Nations has been trying to conduct a technical assessment of the tanker’s condition and perform light repairs, a first step to eventually offloading the oil and towing the ship to a safe location for inspections and dismantling. But the ship, roughly 37 miles northwest of the Yemeni port city of Hodeidah, is moored in waters near areas controlled by Yemen’s northern Houthi rebels.

Today, the United Nations is still awaiting permission from the rebels to visit the ship. Last month, Mark Lowcock, the top U.N. humanitarian official, told the Security Council that the Houthis have finally agreed to allow a U.N. mission to inspect the ship. But Lowcock also noted that the rebels had granted permission in August 2019 only to cancel the mission the night before it was scheduled.

According to Ralby and human rights activists, the Houthis are seeking to sell the oil on the Safer, valued at as much as $40 million at one point, though Ralby and other analysts say the cargo is worth far less now, due to the coronavirus pandemic, the global glut in crude and five years of sitting in corroding tanks. Alternatively, the rebels hope to use the oil as a bargaining tool against the internationally recognized Yemeni government and their primary benefactor, a U.S.-backed Saudi-led coalition that has been fighting the Houthis for more than five years.

This is where any similarities between Beirut and Yemen end, activists say.

“In the case of the Houthis, they are putting 30 million people’s lives and livelihoods and welfare at risk for strategic, military and political reasons,” said Gerry Simpson, associate crisis and conflict director at Human Rights Watch. “In the case of Beirut authorities, it looks like sheer negligence.”

“The Houthis have no interest whatsoever in throwing away strategic advantages in their war against the Saudis,” he added. “The tanker is a negotiating tool to reach their strategic outcome.”

Ameen al-Sharafi, a spokesman for the Houthi-controlled Oil Ministry in the Yemeni capital, Sanaa, denied the allegations and blamed the U.N. and the coalition for the delays in assessing the tanker.

“There is no prevention from our side to maintain and treat any damage to the tanker,” al-Sharafi said.

Built as an oil supertanker in the mid-1970s in Japan, the Safer is officially owned by the Yemeni government and has not been maintained since 2015, when the Iran-aligned Shiite Houthis pushed the government out of the capital. In May, a leak allowed seawater to spill into the engine room, which Lowcock said “brought us closer than ever to an environmental catastrophe.”

Last month, both the British government and senior U.N. officials expressed concerns to the U.N. Security Council.

“Should the situation get out of control, it will directly affect millions of people in a country that is already enduring the world’s largest humanitarian emergency,” said Inger Andersen, the executive director of the U.N. Environment Program. “It will destroy entire ecosystems for decades and go beyond borders.”

It would certainly affect the lives of at least 28 million Yemenis, who are already enduring starvation, disease and the spreading coronavirus. Many rely on the Red Sea’s resources for their livelihoods, and a massive oil spill would destroy “opportunities for fishing and coastal development for generations,” Ralby said.

A U.N.-commissioned study found that an oil spill could harm fisheries along Yemen’s Red Sea Coast, lead to sharp increases in fuel and food prices, cause crop losses and contaminate thousands of water wells. It would also devastate the ecosystems of the Red Sea, an important biodiversity sphere. It would kill hundreds of species of marine mammals, sea turtles and seabirds, as well as destroy pristine coral reefs.

“In this bleak picture, there is one bright spot,” Andersen said. “This disaster is entirely preventable, if we act fast.”