President Donald Trump said in a post on his social media platform Sunday afternoon that the U.S. Navy had attacked an Iranian-flagged cargo ship in the Gulf of Oman and that U.S. Marines have taken custody of the vessel.

“Today, an Iranian-flagged cargo ship named TOUSKA, nearly 900 feet long and weighing almost as much as an aircraft carrier, tried to get past our Naval Blockade, and it did not go well for them,” Trump said in the post.

U.S. Central Command confirmed that the destroyer USS Spruance intercepted the Touska as it transited the North Arabian Sea towards the Iranian port of Bandar Abbas. 

After repeated warnings over a six-hour timespan, the destroyer warned the Touska’s crew to vacate the engine room and fired several rounds at that location from its five-inch gun, according to CENTCOM.

Marines later boarded the ship, and it remains in U.S. custody, CENTCOM said.

It appears to be the first instance of the U.S. attacking and seizing a merchant vessel since it instituted the blockade of Iranian ports.

The president further wrote that “U.S. Marines have custody of the vessel,” which he said is “under U.S. Treasury Sanctions because of their prior history of illegal activity. We have full custody of the ship, and are seeing what’s on board!”

The move comes after Joint Chiefs Chairman Gen. Dan Caine warned that the U.S. would actively enforce the blockade on Iranian-flagged vessels around the globe.

“In addition to this blockade, the joint force, through operations and activities in other areas of responsibility, like the Pacific area of responsibility under the command of Admiral Paparo, will actively pursue any Iranian-flagged vessel or any vessel attempting to provide material support to Iran. This includes Dark Fleet vessels carrying Iranian oil,” Caine said in a Pentagon press conference Thursday.

-ABC News’ Nicholas Kerr