Japan is asking the United States and South Korea to help watch for ship-to-ship transfers of fuel and other goods in the East China Sea that violate U.N. sanctions against North Korea, government sources said.

Japan is the only country watching over ship-to-ship transfers extensively involving North Korean vessels in the waters, the sources said Sunday. The Maritime Self-Defense Force and the Japan Coast Guard are engaged in the mission but want other countries to participate as well.

"If Japan, the United States and South Korea will lead efforts to crack down on ship-to-ship transfers, it will be easier to seek cooperation" from the entire global community, a senior Foreign Ministry official said in Tokyo.