TOKYO (Reuters) – Japan has told the United Nations about a North Korean tanker spotted in the East China Sea that it suspects was engaged in a transfer of goods with another tanker in defiance of U.N. sanctions, the Foreign Ministry said on Wednesday.

North Korea’s development of nuclear weapons and missiles capable of hitting the United States has spurred deepening U.N. Security Council sanctions and stoked fears of a military conflict.

According to a statement issued by the Foreign Ministry, the North Korean-flagged tanker “Rye Song Gang 1” – blacklisted by the United Nations last month for carrying banned cargo – was spotted by a Japanese Maritime Self Defence Force patrol plane with the Dominican-flagged tanker “Yuk Tung” tied up beside it in the East China Sea on Saturday.

The two boats were lit up and some kind of activity was taking place, the Foreign Ministry said, adding that the Japanese government strongly suspected them of transferring goods in violation of the U.N. sanctions.

It did not specify what goods it suspected were being transferred. The U.N. Security Council in December unanimously imposed new sanctions on North Korea for a recent intercontinental ballistic missile test, seeking to further limit its access to refined petroleum products and crude oil.

The ministry also said it appeared that the North Korean-flagged vessel, one of four additional vessels recently denied international port access by the United Nations for breaching sanctions, had disguised its name so that it read “Song Hae.”

“We have reported this to the U.N. and also given this information to other nations involved, including those connected to the Dominican tanker, expressing our concern,” the ministry added.

Diplomats from Dominica, a tiny Carribean island which suffered widespread damage in a hurricane in September, were not immediately available for comment.

North Korea is developing missile and nuclear technology in defiance of international condemnation amid regular threats to destroy the United States, Japan and South Korea.

But tensions have eased with North Korea agreeing to take part in the Winter Olympics in the South next month.

(Reporting by Elaine Lies and Kiyoshi Takenaka; Editing by Nick Macfie)