A green turtle died as oil reached the southern Amami-Oshima Island coast, the local government said Thursday, but it was not clear whether the oil came from an Iranian tanker that sank in nearby waters last month.

The International Union for Conservation of Nature classifies the green turtle as an endangered species.

Clumps of oil were found washed up on the shores of Amami-Oshima Island and Yaku Island over the past week. Environment Ministry officials and the Kagoshima Prefectural Government carried out cleanup efforts Thursday on Amami-Oshima Island.

The Japan Coast Guard’s regional headquarters has said it has not been able to confirm a link between the pollution and the oil spill following the tanker collision on Jan. 6. It will continue investigating the incident.

The prefectural government began investigating the cause of the turtle’s death after it was found on Tuesday. Oil was found stuck to the inside the turtle’s mouth, officials said.

In last month’s accident, the Panama-registered tanker Sanchi was sailing from Iran to South Korea carrying 136,000 tons of oil condensate — an ultralight type of crude oil that evaporates. It collided with a cargo ship off Shanghai.

The tanker burst into flames and drifted into Japan’s exclusive economic zone in the East China Sea. It was about 315 km west of Amami-Oshima Island before sinking in mid-January.

The Sanchi is also believed to have been carrying about 2,120 tons of heavy oil to use as fuel, the coast guard said.

KEYWORDS pollution, accidents, oil, Kagoshima, sanchi