Abu Dhabi, UAE(CNN) Iran has seized an oil tanker it claimed was carrying 1 million liters of "smuggled fuel," state news agency Press TV said on Thursday, before later releasing a video purporting to show the tanker.

The semi-official Fars news agency said Islamic Revolutionary Guard Corps (IRGC) forces ambushed the tanker, carrying 12 people on board, on Sunday.

The IRGC said it had initially responded to distress calls from a ship on Sunday but when they searched it, they discovered it was a smuggling operation, according to Iranian state media.

The footage released by Press TV later on Thursday shows two smaller vessels maneuvering around a larger ship, with clear markings saying "RIAH" and "Panama." It is not clear when the video of the tanker was filmed.

Since the weekend, US intelligence have been investigating what happened to the Panamanian-flagged tanker M/T RIAH.

The ship-tracking website Marine Vessel Traffic has not had a current location for the tanker since July 7.

After US intelligence raised fears that the ship had been forced into Iranian waters last weekend, Iran said on Wednesday that it had assisted one vessel suffering a technical glitch.

A screengrab from Iran's state-run Press TV showing IRGC's purported seizure of the M/T RIAH.

It remains unclear who owns the ship.

While the initial US intelligence suggested that the tanker was UAE-owned, the United Arab Emirates has said that the tanker in question was "neither owned nor operated by the UAE. It does not carry Emirati personnel, and did not emit a distress call," according to state-run WAM.

Citing an IRGC statement, Fars descibed the ship as a foreign tanker that was seized in an area south of Larak, a small island in the Strait of Hormuz.

Fars added that the ship was carrying fuel smuggled to it on Iranian dhows, or small boats.

The IRGC have denied seizing any other tankers, Fars said Thursday.

In a statement on Thursday, a US State Department official said the US "strongly condemns the Islamic Revolutionary Guard Corps Navy's continued harassment of vessels and interference with safe passage in and around the Strait of Hormuz."

"Iran must cease this illicit activity and release the reportedly seized crew and vessel immediately," they said, adding that the US will "continue to work closely with our allies and partners to ensure the Iranian regime's extortion tactics and malign activities do not further disrupt maritime security and global commerce."

Recent incidents

The ship's seizure is one in a series of recent maritime episodes involving Iran.

On Thursday morning, the US Navy destroyed an Iranian drone using electronic jamming, a US defense official told CNN. The crew of the USS Boxer took defensive action against the Iranian unmanned aerial vehicle after it came close to the US naval ship, the official said.

Chief Pentagon Spokesperson Jonathan Hoffman said that the USS Boxer had been in international waters where it was "conducting a planned inbound transit of the Strait of Hormuz."

US President Donald Trump said the Iranian drone was "threatening the safety of the ship and the ship's crew" and was "immediately destroyed."

The US "reserves the right to defend our personnel, our facilities and interest and calls upon all nations to condemn Iran's attempts to disrupt freedom of navigation and global commerce," Trump added.

"We have no information about losing a drone," Iran's Minister of Foreign Affairs Mohammad Javad Zarif said Thursday.

In another incident last week, armed Iranian boats tried unsuccessfully to impede the passage of a British oil tanker in the Persian Gulf, according to two US officials with direct knowledge of the incident.

In June, tensions between the US and Iran escalated into a military standoff after an American drone was shot down by Iran over the Strait of Hormuz, one of the world's most vital shipping routes.

On Wednesday, the head of the IRGC, Commander Hossein Salami, warned that Iran will change from its current defensive strategy to an offensive one "if the enemy makes a mistake," according to reporting by Iran's semi-official Tasnim News Agency.

Salami said "we are operating with a defensive strategy" and that "we will not initiate any wars," Tasnim reported.

He also emphasized the preparedness of Iran's naval forces "to secure Iran's territorial waters" if needed, according to Tasnim. Salami made the comments while touring the strategic and disputed "Three Islands," located near the Strait of Hormuz in the Persian Gulf.

This story has been updated with new reporting from Iranian state media about the amount of oil on board the vessel.