It was not immediately clear what had caused the apparent spill, which was located off the island’s west coast.
It appeared to cover more than 52 square kilometres as of Thursday, according to an estimate by Orbital EOS, which monitors oil spills.
The slick appeared to be spreading southward toward Saudi waters.
Kharg Island is at the heart of Iran’s oil export industry, a lynchpin of the country’s battered economy, and lies in the Gulf, north 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, stranding many tankers in the area.
Kharg Island has Iran’s largest oil terminal, oil pipelines, storage tanks and related infrastructure. (AFP)
