A Japanese patrol plane spotted a Dominican Republic tanker apparently transferring fuel to a North Korean vessel in the East China Sea in violation of UN sanctions.

A Maritime Self-Defence Force (MSDF) aircraft took photographs of the encounter, which took place in waters near Shanghai, Japanese government sources told Kyodo News.

The information has since been passed on to the United States’ government, Japan’s key ally in enforcing a growing list of sanctions against North Korea, Kyodo News reported.

The Japanese government has vowed to take tougher measures to prevent North Korea from circumventing international sanctions.

Taro Kono, the foreign minister, told a news conference: “North Korea is becoming more skilled at escaping sanctions. We will take a co-ordinated response to it internationally.”

The Japanese P-3C aircraft was reportedly engaging in patrol activities at the time of the incident, specifically looking out for the illicit transfer of refined oil at sea by North Korea.

At the request of the US, Japan’s MSDF vessels and aircraft have been conducting patrols in its surrounding waters, in order to clamp down on potential violations of international sanctions.