Coast Guard Tracks Down a Runaway Oil Tanker Linked to Iran and Venezuela

The U.S. is gathering more manpower and weaponry to seize the sanctioned Bella 1 as it flees in the Atlantic.

A Coast Guard vessel was slicing through the Atlantic Ocean, with its target in sight just a half mile away, when a realization set in. The crew was going to need backup, U.S. officials said.

A U.S. Coast Guard helicopter flying over Puerto Rico last week.

The Bella 1, an oil tanker far larger than any Coast Guard ship, has been fleeing the U.S. blockade of sanctioned vessels heading in and out of Venezuela. Sanctioned for allegedly shipping oil to U.S.-designated terrorist organizations, the Bella 1 made an unusual move last weekend, executing a U-turn, refusing to be boarded and racing away from Venezuela at full speed.

Now, more than five days into the pursuit, the Coast Guard and U.S. military are assembling more manpower and weapons to forcibly board the vessel, the U.S. officials said. Among the units they are moving to the area is a Maritime Special Response Team, an elite force trained to board hostile ships, the officials said.

The hunt for the Bella 1 marks potentially the most dangerous moment yet for the U.S. in its nascent quarantine of the Venezuelan oil industry, part of a campaign to squeeze the country’s leader, Nicolás Maduro, whom the Trump administration accuses of flooding the U.S. with drugs. Maduro denies the charges and accuses Washington of naval piracy and trying to steal his country’s natural resources.

The U.S. military has built up considerable firepower in the Caribbean for the first time in decades, conducting deadly strikes on boats allegedly carrying drugs and now targeting oil tankers.

The U.S. has seized two tankers carrying Venezuelan oil since Dec. 10, aiming at Maduro’s most important source of revenue. Neither crew resisted.

It isn’t publicly known why the Bella 1 is refusing the Coast Guard’s demands. The Bella 1’s owner, Turkey-based Louis Marine Shipholding Enterprises, didn’t return calls seeking comment.

Most commercial seafaring vessels, even those carrying illicit products, are staffed by crews with little incentive to disobey the orders of the U.S. armed forces.

The U.S. has sanctioned it for allegedly carrying black-market Iranian oil on behalf of U.S.-designated terrorist organizations aligned with Tehran, the Lebanese militia Hezbollah and the Houthis, the rebels who have controlled swaths of Yemen for more than a decade. The U.S. Treasury says the Bella 1 has links to the Quds Force, the foreign arm of Iran’s Islamic Revolutionary Guard Corps, a powerful paramilitary and business entity.

“They are probably getting orders from somewhere,” Rear Adm. William Baumgartner, a former judge-advocate general in the Coast Guard, said of the unusual behavior of the ship’s crew. “These are owned by very bad people trying to make money in a particular manner.”

The U.S. says the Bella 1 is part of a vast fleet of aging oil tankers, with murky ownership, that connect U.S.-sanctioned oil from Russia, Iran and Venezuela to buyers in China, Cuba and India, among others.

The Bella 1 has long used tactics associated with the so-called shadow fleet, including switching off its transponders—which alert other ships to its location—for long periods, and conducting dangerous ship-to-ship oil transfers on the high seas, according to Kpler, a tanker tracking firm. Those sorts of ship-to-ship transfers, U.S. officials say, are usually done to conceal the oil’s illicit point of origin. Like other shadow-fleet ships, the Bella 1 alo sailed under a false flag, saying it was registered in Guyana when it isn’t, U.S. officials said.

Before heading toward Venezuela, empty of oil, the Bella 1 loaded crude in Iran in early September, Kpler said, and then turned off its transponder near the Strait of Hormuz, the narrow waterway linking the oil-rich Persian Gulf to the world. It went dark for two months, and when it came back online close to the same spot, it was no longer carrying oil, Kpler said, suggesting it had unloaded the cargo to other vessels.

The Bella 1 then headed west, crossing the Strait of Gibraltar and into the open Atlantic in early December, according to Kpler. It signaled a destination of Curaçao, just off the coast of Venezuela, but then suddenly reversed course on Dec. 15, Kpler said, after the U.S. seized its first ship of the quarantine. It then turned back toward Venezuela, Kpler said, but made another U-turn when engaged by a Coast Guard vessel.

There is no rush to conduct an operation against the Bella 1, a slow-moving vessel that cannot outrun U.S. forces now that its location is known, U.S. officials said. That has given the U.S. time to deploy the appropriate units, explaining why the chase has stretched over several days.

In addition to relocating elite forces, Baumgartner said, the Coast Guard may also be bringing in a captain qualified to pilot a ship of such vast size—about three football fields long and almost 20 stories tall.

Once everything is in place, he said, the U.S. would have the right under international law to use force to board the Bella 1, beginning with a graduated series of warnings that could include warning shots.

“They will have multiple helicopters, they will fast-rope into the tanker, and they’ll go up to the bridge, and they’ll take control of the vessel,” he said about a likely scenario.

The White House said the Bella 1 was under a judicial order allowing the U.S. to seize it, part of a Justice Department strategy to take the dark fleet of oil tankers out of operation. Assuming the ship is ultimately seized, the U.S. plans to escort it to American waters and take the oil, officials said.

That follows a similar pattern to how the U.S. has treated other seized tankers. The Centuries, a tanker carrying about two million barrels of Venezuelan oil, was seized last week and is now headed toward Galveston, Tex., where its oil will be unloaded, officials said. Trump said the U.S. would keep the oil and the ships.

Countries can legally seize vessels in their territorial waters under rules set by the International Maritime Organization, the United Nations maritime regulator. Seizures on the high seas are far rarer—especially when vessels are tied to Iran—because Tehran has a record of retaliating by detaining Western ships.

A U.S. military helicopter flies over the Centuries oil tanker, which was intercepted by the U.S. Coast Guard.

Write to Shelby Holliday at shelby.holliday@wsj.com, Costas Paris at costas.paris@wsj.com and Lara Seligman at lara.seligman@wsj.com