South Korea is investigating a ship suspected of violating U.N. sanctions against North Korea, which was reportedly seized over the weekend, Seoul’s Foreign Ministry said on Wednesday.

The investigation comes after Moscow last week used its veto power to effectively end official U.N. oversight of sanctions on North Korea, as well as an investigation into alleged arms transfers between Moscow and Pyongyang.

South Korean authorities seized a 3,000-ton cargo ship named “DEYI” in waters off the country’s south coast on Saturday, Seoul’s Yonhap News Agency reported. The ship was not registered in any country.

The attack was reportedly carried out “en route from North Korea to Russia via China,” the agency’s report said, citing security sources.

“Our government is working closely with the United States to investigate the ship’s suspected violation of Security Council sanctions resolutions,” Seoul’s Ministry of Foreign Affairs said in a statement.

“As the investigation is currently ongoing, it is difficult to provide details,” it added.

According to Yonhap News Agency, there were 13 people on board, including a Chinese captain and Chinese and Indonesian crew members.

Since 2006, the United Nations Security Council has imposed increasing sanctions over North Korea’s nuclear program.

North Korea’s traditional allies Russia and China have been trying to persuade the Security Council to ease open-ended sanctions since 2019.

Pyongyang has moved to take advantage of the UN standoff, ramping up missile testing and weapons development and declaring that it will become an “irreversible” nuclear power by 2022.

Experts say Russia’s recent end to United Nations oversight is a major victory for North Korean leader Kim Jong Un.