WASHINGTON--North Korea is still able to skirt U.N. sanctions by using ships registered in other nations to swap cargo on the high seas and smuggle much-needed petroleum to the impoverished nation.

The cat-and-mouse game playing out between North Korea and the international community raises questions about whether China and Russia are turning a blind eye to this activity.

The U.N. Security Council keeps tightening economic sanctions against North Korea in an effort to force Pyongyang to the negotiating table to renounce its ballistic missile launches and nuclear tests.

But according to government sources in Japan, the United States and South Korea, the U.S. military has confirmed that North Korea is using ships registered in the African nations of Tanzania and Togo, among others, as well as the Pacific island nation of Palau, to transfer cargo at sea.

Those ships are being used to export North Korean coal to Russia, China and other nations and to import petroleum and its by-products into North Korea.

Between October and December, the U.S. military used various means, including Navy ships, to confirm that North Korean ships were transferring cargo to and from other ships in the East China Sea and South China Sea.

It is not clear if China and Russia are in cahoots with North Korea, but at the very least they are thought to have a behind-the-scenes role in ensuring that petroleum and refined petroleum products are transferred to North Korean ships.

A U.N. Security Council resolution in September banned the transfer of cargo to North Korean ships on the open seas. In December, another resolution was approved to reduce exports of refined petroleum products to North Korea by 90 percent.

Foreign-registered ships being used to exchange cargo at sea are also taking measures to avoid detection by the U.S. military and other agencies as they approach their destinations. For one thing, those vessels appear to be turning off their automatic identification system (AIS), a tracking system that electronically informs other ships of the position and speed of the beeping ship.

International treaties obligate all ships to keep their AIS active when at sea, but the ships being used by North Korea for smuggling seem to pay no heed.

U.S. officials believe that North Korea is desperate for fuel for use in the development of its nuclear weapons and ballistic missiles, as well as foreign currency earned from exports to keep those programs going.

According to sources, the U.S. military in December asked the Self-Defense Forces and South Korean military to intensify their surveillance of North Korean ships by deploying aircraft and ships to nearby waters.

Against this background, a meeting of foreign ministers will be held Jan. 16 in Vancouver to discuss issues related to North Korea.

U.S. Secretary of State Rex Tillerson is expected to ask other participating nations to strengthen cargo inspections on the open seas to crack down on smuggling by North Korea.

Twenty nations will attend the Jan. 16 meeting co-hosted by Canada and the United States. U.S. officials are expected to call for strengthened pressure on North Korea through the full implementation of U.N. Security Council resolutions.