Iran's coast guard has seized a foreign tugboat and detained its 12 Filipino crew members, state television reported on Saturday.
It said the tugboat was carrying nearly 284,000 liters (75,000 gallons) of diesel. The report did not say what national flag the vessel was flying.
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Iran, which has some of the world's cheapest fuel due to heavy state subsidies, has been fighting rampant fuel smuggling overland to neighboring countries and by sea to Gulf Arab states. It has frequently seized boats that it says are being used for smuggling fuel in the Gulf.
The incidents come at a time of increased tensions between Iran and the West in the Gulf following the United States' exit from the 2015 nuclear deal with Tehran.
While Iranian media reports say that an estimated 10 million liters (around 2,600,000 gallons) of fuel are smuggled per day, Tehran has been promoting legal gasoline exports through its energy exchange.
Gasoline sales hit a record high of $72 million last week on the Iran Energy Exchange for exports to neighboring countries, according to state TV.
The stand-off between Iran and the United States triggered by Washington's withdrawal from the 2015 nuclear deal with Tehran in May last year has stirred fears of a Gulf war with global repercussions.
In July, Iran seized a British oil tanker near the Strait of Hormuz for alleged maritime violations, two weeks after British forces detained an Iranian tanker near Gibraltar accused of taking oil to Syria in violation of European Union sanctions.
The Iranian tanker was later released and was last spotted off the coast of Syria. This week, Iran freed seven of the 23 crew members of the British-flagged oil tanker.
