The most public display of the deepening relationship: five oil tankers now steaming across the Atlantic Ocean, carrying what analysts estimate to be 60 million gallons of Iranian gasoline, which they say was bought with Venezuelan gold, an allegation Iran denies. The first of the ships is set to arrive in Venezuelan waters as soon as this weekend, to relieve fuel shortages so dire that the sick can’t get to hospitals and produce is rotting on farms.

“You have two pariah states finding that they are able to exchange things they need for things they have,” said Elliott Abrams, U.S. special representative to Venezuela.

U.S. sanctions on Iran target anyone purchasing or facilitating the purchase of petroleum products from that country, but Venezuela’s oil company is already under similar sanctions. The Trump administration has also invoked the Monroe Doctrine — the 19th-century policy that rejects outside intervention in the Western Hemisphere — to move against foreign entities that do business with Maduro.

Iran is warning against any U.S. effort to board or blockade the vessels, and Venezuela is vowing to deploy warships to escort the convoy through its territorial waters.

Washington has countered by sounding an alarm over Iran’s growing involvement in Venezuela. U.S. officials say they are monitoring the convoy, but tempering talk of direct engagement.

The voyage is testing how far the Trump administration is willing to go to shut down a budding relationship between two nations it considers enemies.

“My sense is that Iranians are willing to use their tankers and play a game of chicken” with the United States, said Evan Ellis, a professor of Latin American studies at the U.S. Army War College.

For Iran, exporting oil to allies has grown more difficult. In August, authorities in Gibraltar, backed by British forces, seized an Iranian supertanker carrying 2.1 million barrels of light crude. Officials said they suspected it was headed to the Syrian port of Baniyas, in violation of European Union sanctions.

Any U.S. interdiction of the convoy now sailing the Atlantic would be challenged by the Iranians and Venezuelans. But Venezuela’s U.S.-backed opposition is providing some possible ammunition with claims the Iranians could be transporting more than mere gasoline.

Opposition leaders have warned that Tehran could be providing materials for what they describe as a covert operation to help Maduro’s intelligence apparatus construct a listening post in northern Venezuela to intercept aerial and maritime communications.

“For Iran, an enemy of the United States, this means they are almost touching America’s tail,” said Iván Simonovis, security commissioner for Juan Guaidó, the Venezuelan opposition leader recognized by the United States as the nation’s rightful leader.

Maduro’s communications minister dismissed those claims as “absurd.”

“It’s a smokescreen by Simonovis,” Jorge Rodríguez wrote in a text to The Washington Post. “Venezuela and Iran have had 20 years of commercial relations and cooperation.”

The nearest of the tankers, the Fortune, was about 800 miles from the Venezuelan refinery complex at El Palito on Saturday afternoon. The convoy was heading toward the largest U.S. military presence in the Caribbean in at least a decade. The Pentagon has dispatched destroyers, littoral combat ships, Poseidon maritime planes and Air Force surveillance aircraft to the region as part of an operation to shut down drug-trafficking routes off the Venezuelan coast.

U.S. officials are downplaying Iran’s suggestion that those forces will confront the convoy. Pentagon spokesman Jonathan Hoffman told reporters Thursday he was not aware of plans to launch a military operation against the Iranian tankers.

But a senior Trump administration official, speaking on the condition of anonymity to describe internal discussions, said the administration “would not abide” Iran’s support of Maduro.

“The president has made clear the United States will not tolerate continued meddling by supporters of an illegitimate regime,” the official said. The administration considers Maduro a usurper, saying he stole the presidential election in 2018; the Justice Department indicted him in March on narcoterrorism charges. The United States is one of nearly 60 nations that recognize Guaidó, head of Venezuela’s National Assembly, as the country’s lawful leader.

“The importation of Iranian gasoline is an act of desperation by the corrupt & illegitimate Maduro regime,” President Trump’s National Security Council tweeted Thursday. “It will not stop Venezuela’s chronic fuel shortages or alleviate the suffering that Maduro has inflicted on the once prosperous people of his country.”

Analysts say the administration is more likely to use additional economic sanctions than force to deter Iranian-Venezuelan trade. While Trump has staked out hawkish positions on Iran — pulling out of the 2015 nuclear deal, imposing punishing sanctions and authorizing the January killing of the military commander Qasem Soleimani — he has at other times demonstrated a desire to avert major conflict.

As the Iranian tankers were headed west last week, the State and Treasury departments and the U.S. Coast Guard issued a global advisory to the maritime industry, warning that nations including Iran might be engaging in “deceptive shipping practices” to evade sanctions.

Adm. Craig Faller, commander of U.S. Southern Command, said this week that he believed Iran’s objective was to “gain positional advantage in our neighborhood in a way that would counter U.S. interests.”

“We have seen an uptick in Iranian state-sponsored activity and liaison with Venezuela that has included Quds Force” — an elite Iranian military unit — “and it has included other elements of support to the illegitimate Maduro regime cronies,” he said during a video briefing on Monday with Florida International University.

Venezuela’s strategic ties to Iran date back almost two decades, when President Hugo Chávez, the founder of its socialist state, struck a flurry of economic and financial deals with a fellow thorn in America’s side — Mahmoud Ahmadinejad, then the president of Iran.

Many of those deals were propaganda on paper that never truly materialized. But with both countries now under crippling U.S. sanctions and confronting painful recessions amid the coronavirus outbreak and collapsing oil prices, they are moving to solidify mutually beneficial bonds.

Maduro is struggling to keep the lights on, literally, in a country plagued by frequent and widespread blackouts, on top of shortages of gas, food, water and medical supplies. In recent months, his most critical problem has been the lack of gasoline.

Venezuela, an OPEC state, boasts the world’s largest oil reserves. But years of mismanagement and corruption — and, more recently, U.S. sanctions on its all-important oil sector — have combined to leave its petroleum industry in tatters and its gas refineries in disrepair. Maduro’s traditional backers, Russia and China, have seemed increasingly reluctant to bail him out. The Russian state-controlled oil giant Rosneft divested itself of its Venezuela operations in March and has backed off oil deals with Maduro that included shipping Venezuela desperately needed gas.

Iran, also under tough U.S. sanctions, has far less to lose.

Last month, aviation tracking firms registered more than a dozen special flights to Venezuela by Mahan Air, sanctioned by the United States for allegedly transporting weapons and operatives of the Iranian military abroad, including to Syria in support of Syria’s Bashar al-Assad.

Iranian President President Hassan Rouhani warned Saturday the United States could face unspecified “trouble” if the tankers cannot reach their destination, Iran’s Mehr news agency reported.

Russ Dallen, a partner in Caracas Capital Markets, a Florida-based company that monitors Venezuela’s energy sector, said information collected by the firm indicated the flights were carrying chemicals and equipment to help Venezuela restart its moribund domestic gas refineries. Maduro’s government, he said, appears to have paid for those parts — as well as the Iranian gasoline now in transit — with gold from the Central Bank.

“We track Central Bank reserves every month,” Dallen said. “They suddenly went down from April to May by $700 million.”

Iran’s ambassador to Venezuela, Hojjatollah Soltani, denied any gold-for-gas deal with Maduro. He said this week that the two nations had the right to engage in regular bilateral trade.

“This relationship between Iran and Venezuela doesn’t threaten anybody,” Soltani told reporters Wednesday at the Iranian Embassy in Caracas. “It’s not a danger to anyone.”

Faiola reported from Miami, Ryan from Washington and Cunningham from Istanbul. Mariana Zuñiga and Ana Vanessa Herrero in Caracas and Carol Morello and John Hudson in Washington contributed to this report.