Iran’s oil infrastructure may be the source of a suspected slick off a key island export terminal, but satellite images showed it was “much reduced” Saturday, an environmental group said.

Satellite images in past days appeared to show an oil slick spreading off the coast of the Islamic Republic’s Kharg Island.

It was not immediately clear what had caused the apparent spill off the west coast of the small Gulf island.

“The cause and origin of the slick remain unknown and cannot be determined conclusively from the available imagery alone,” a UK-based non-governmental organisation, the Conflict and Environment Observatory, told AFP.

“While offshore infrastructure in the wider area could be a potential source, we are unable to identify a definitive point of origin or attribute the spill to a specific cause at this time,” said Leon Moreland from the observatory.

But he added “the slick appears visually consistent with oil based on analysis” of imagery from the Copernicus Data Space browser.

Some media reports, including by Fox News, suggested Iran’s oil storage facilities may be coming under strain as a US naval blockade disrupts the country’s ability to export or store crude.

Moussa Ahmadi, head of the Iranian parliament’s energy commission, told ISNA news agency on Saturday there was “no official report so far confirming” that Iran’s oil facility was leaking due to strained storage facilities.

“Production in various oil fields in the country continues incessantly and without any problem,” he said.

Earlier, Jafar Pourkabgani, a lawmaker representing the coastal city of Bushehr, dismissed the reports as “false”.

“The stains observed in satellite images around the resilient Kharg Island are related to oil and ballast water waste from oil tankers, which was dumped into the sea by a European oil tanker to the detriment of the environment,” he said, according to state television.

Moreland said there was “no obvious evidence of additional active spills around the island, although the earlier slick can still be observed moving south”.

Copernicus images on Saturday appeared to show that the suspected slick was “much reduced” from the first pictures seen on Wednesday, the observatory added.

It put the spread of the original slick at about 44 square kilometres (17 square miles).

But Orbital EOS, which monitors oil spills, told The New York Times the spill appeared to cover more than 20 square miles (52 square kilometres) as of Thursday.

Kharg Island is at the heart of Iran’s oil export industry, a lynchpin of the country’s battered economy. It sits off Iran’s Gulf coast, hundreds of kilometres northwest of the narrow, strategic Strait of Hormuz.

Iran largely closed the strait at the start of its conflict with the United States and Israel on February 28. The United States has since imposed a blockade of Iranian ports. Many tankers are stranded in the area as a result of both blockades.