Iran arrested 12 Filipinos as it busted a "fuel-smuggling ring" in the Strait of Hormuz. (AFP photo)

Iran seized a boat and arrested 12 Filipinos as it busted a "fuel-smuggling ring" in the Strait of Hormuz on Saturday, the semi-official news agency ISNA reported.

"A foreign tugboat was confiscated as well as 283,900 litres (75,000 gallons) of petrol worth 233.71 billion rials (about $2 million)," ISNA said, citing the coast guard chief in the southern province of Hormozgan.

"Twelve Philippine nationals were arrested and the relevant judiciary officials are currently taking the required legal measures," Major Hossein Dehaki was quoted as saying.

Dehaki said the group was suspected of operating a fuel-smuggling ring and the confiscated shipment had been intercepted close to Sirik county in the Strait of Hormuz.

The seizure comes amid tensions in the Gulf after the United States unilaterally withdrew from a nuclear deal putting curbs on Iran's nuclear programme in return for relief from sanctions.

The escalation has seen ships mysteriously attacked, drones downed and oil tankers seized in the Strait of Hormuz -- a chokepoint for a third of world's seaborne oil.

Iran's Islamic Revolutionary Guard Corps detained a "foreign tanker" in Gulf waters on July 14 for allegedly smuggling contraband fuel.

"With a capacity of two million litres and 12 foreign crew on board, the vessel was en route to deliver contraband fuel received from Iranian boats to foreign ships," the Guards said at the time.

Maritime tracking service TankerTrackers reported the Panamanian-flagged MT Riah, used in the strait for fuelling other vessels, had crossed into Iranian waters, and at that point its automatic identification system stopped sending signals.

In the most high-profile seizure, the Guards impounded the British-flagged Stena Impero tanker in the Strait of Hormuz on July 19 for breaking "international maritime rules".

Iran also seized another ship on July 31 with seven foreign crew onboard over fuel smuggling, but it has not revealed the vessel's identity or the nationality of its crew.