Oil that has washed ashore on several southern Japanese islands is likely from an Iranian tanker that sank in the East China Sea last month, Japan's coastguard said Friday.
Analysis of samples of heavy fuel that began washing up on remote Okinoerabu and Yoron islands this month found similar components to the fuel used by the Sanchi tanker, coastguard spokesman Takuya Matsumoto said.
"We are not aware of any other maritime accident in the region that resulted in oil leaks," he told AFP.
"So we have concluded that it is highly likely that the oil that reached (the two islands) is connected with Sanchi," he said.
The sunken ship—carrying 111,000 tonnes of light crude oil—went down in a ball of flames on January 14 in Japan's economic waters in the East China Sea, sparking concerns it could lead to a massive environmental catastrophe.
Late January, greasy sludge began to wash up on remote Japanese islands, known for seafood and pristine shores that lure holidaymakers.
The oil washing ashore differs from the light crude that was the ship's cargo and is likely to be the fuel that was powering the vessel.
At least 16 islands in the area saw oil reach their shores, and residents have collected a total of 90 tonnes of oil in their cleanup efforts, according to the local government.
Tokyo has launched detailed studies of the accident's impact on the regional environment, although coastguard officials believe the leaking light crude oil is gradually dissipating.
Oil samples from other islands showed different characteristics, but the tanker could have used various kinds of heavy oil in different tanks and equipment, Matsumoto added.
"We are continuing our analysis. We believe it is premature to reach any conclusion about the oil coming to other islands," he said.
Reviews of water samples collected in the region have not shown elevated levels of contamination, the coastguard said.
The government has launched studies to analyse the accident's impact on the region's fisheries as well as ecosystems, including impacts on birds and coral reefs.
The Sanchi caught fire after colliding with a bulk freighter in early January, setting off a desperate rescue mission by authorities. The bodies of only three of its 32 crew have been found so far.
Environmental campaign group Greenpeace has urged authorities to boost clean up efforts and monitoring of regional waters.
The type of condensate oil carried by the Sanchi does not form a traditional surface slick when spilt, but is nonetheless highly toxic to marine life and much harder to separate from water.
Explore further: 'Oil-like' blobs hit Japan beaches after tanker sinks