Iran’s Revolutionary Guards said Saturday they had seized an oil tanker off the country’s coast, a day after maritime security firms suggested the force was behind the interception.

“Yesterday morning at 7:30, after a judicial authority ordered the seizure of the cargo of an oil tanker with the trade name Talara and the flag of the Marshall Islands, the Islamic Revolutionary Guard Corps (IRGC) rapid reaction units of the naval forces monitored its movements and intercepted and seized it,” said a statement from the IRGC, the ideological arm of the Islamic republic’s military.

“The tanker was found to be in violation of the law by carrying unauthorized cargo,” the statement continued, adding it “was carrying 30,000 tons of petrochemical cargo and was heading to Singapore”.

The vessel had departed from Ajman in the United Arab Emirates and was heading south through the Strait of Hormuz when it was approached by three small boats, after which it made a “sudden course deviation”, maritime security company Ambrey said.

The U.S. Navy had earlier said it was “actively monitoring the situation”.

“Commercial vessels are entitled to largely unimpeded rights of navigation and commerce on the high seas,” said the U.S. 5th Fleet, which patrols the region.

The Strait of Hormuz, a vital waterway for global oil and liquefied natural gas, has previously been the scene of similar incidents.

Last year, the Revolutionary Guards seized a container ship, saying it had links to Israel, following a deadly attack on Iran’s consulate in Syria blamed on Israel.