TOKYO: Oil that reached islands in southern Japan earlier this month is highly likely to have come from the sunken Iranian tanker Sanchi, the Japan Coast Guard said on Thursday.

Samples of oily matter that washed up on February 8 on the shores of the Okinoerabu and Yoron islands in the Amami chain were found to be linked to the Sanchi's sinking, the Coast Guard said.

The Sanchi sank on January 14 after colliding with a freighter on Jan. 6 in the world's worst oil tanker disaster in decades.

"Oily matter that arrived at the shores of the two islands is extremely likely to be linked to the Sanchi tanker incident, considering the similarity of the oil and the fact that there has not been any marine disaster involving oil spill in the nearby sea area," a Coast Guard official told Reuters by phone on Thursday.

Black clumps of oily matter first washed up on the shores of Takarajima island on January 28 and other matter has since arrived at 21 other islands in southwestern Japan that are part of a chain of islands that includes Amami-Oshima and Okinawa, areas famous for pristine beaches and reef systems.

The Sanchi, which the Coast Guard said was carrying 111,000 tonnes, or about 810,000 barrels, of condensate - an ultra-light, highly flammable crude oil - sank after several explosions weakened the hull following the collision.

Most of the fuel evaporated after the ship caught fire.

The bodies of two sailors were recovered from the ship while a third body was pulled from the sea near the vessel. The remaining 29 crew of the ship are presumed dead.

On January 17, the Chinese government said the sunken tanker had created two oil slicks.

Japan's environment ministry said in January it saw little chance that the spill would reach Japanese shores.

Seawater samples taken from January 29 to February 2 at 14 different locations offshore southern Japan detected no oil pollution from the sunken tanker, the Coast Guard said in a statement on Wednesday.

An oil slick continues to be seen near where the Sanchi sank. The slick is located about 315 km (197 miles) west of Amami-Oshima island and is about 700 metres long and 20 metres wide, though oil has been evaporating from the fringes, the Coast Guard said in a statement on Thursday.

Japanese and Chinese patrol boats have been searching for the missing crew in the area and sailing over the slick to try to dissipate the oil, it added.