Iran is sending its biggest fleet yet of tankers to Venezuela in defiance of U.S. sanctions to help the isolated nation weather a crippling fuel shortage, according to people with knowledge of the matter. Some of the flotilla of about 10 Iranian vessels will also help export Venezuelan crude after discharging fuel, the people said, asking not to be named because the transaction is not public.

The Nicolas Maduro regime is widening its reliance on Iran as an ally of last resort after even Russia and China have avoided challenging the U.S. ban on trade with Venezuela. The country’s fuel crunch follows decades of mismanagement, corruption and under-investment at state-owned Petroleos de Venezuela since the time of Maduro’s late mentor and predecessor, Hugo Chavez.

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The country that was once a top supplier of crude to the U.S. and boasted one of the lowest domestic gasoline prices in the world, now can barely produce any fuel. The last Iranian fuel shipments sent in early October on three vessels are running out, threatening steeper nationwide shortages with hours-long queues at gas stations.

The current fleet under sail is about double the size of the one that first startled international observers in May, crossing a Caribbean Sea patrolled by the U.S. Navy, to be greeted by Maduro himself upon arrival.

“We’re watching what Iran is doing and making sure that other shippers, insurers, ship owners, ship captains realize they must stay away from that trade,” Elliott Abrams, the U.S. special representative for Iran and Venezuela, said in September.

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The oil ministry in Tehran declined to comment on the matter. Messages sent to several officials at PDVSA, as Venezuela’s state oil company is known, weren’t immediately answered.