Senior North Korean economic officials met with the governor of a Russian region along the Pacific coast for discussions on boosting economic cooperation between the countries, North Korean state media said Wednesday.

The meeting in Pyongyang, North Korea's capital, came as concerns have grown in South Korea that the North may be attempting to expand its labor exports to Russia in violation of U.N. Security Council resolutions to generate revenue for its struggling economy and help fund leader Kim Jong Un’s nuclear weapons program.

The official Korean Central News Agency said North Korean officials led by the country’s external economic relations minister, Yun Jong Ho, met with the delegation led by Oleg Kozhemyako, governor of the Primorye region in the Russian Far East, and discussed elevating economic cooperation between the countries to “higher levels.” The report did not specify the types of cooperation that were discussed.

Kozhemyako told Russian media ahead of his visit that he was expecting to discuss expanding cooperation with the North Koreans in agriculture, tourism and trade.

Kozhemyako’s visit extends a flurry of diplomacy between North Korea and Russia this year, highlighted by a summit between Kim and Russian President Vladimir Putin in September, which underscores their aligning interests in the face of separate, intensifying confrontations with the United States.

Read: South Korea says Russian support likely enabled North Korea to successfully launch a spy satellite

The U.S. and South Korea have accused North Korea of supplying Russian with artillery shells and other weapons over the past months to help it wage war on Ukraine, although both Russia and North Korea have denied such transfers.

There are also concerns that North Korea is preparing to send workers to Russia to secure badly needed foreign currency, which would run afoul of U.N. Security Council sanctions imposed on the North over its nuclear and ballistic missile programs.

The U.S. government announced on Tuesday it was imposing sanctions on more than 250 individuals and entities in connection with Russia’s war on Ukraine, including several shipping companies the State Department said were involved in transferring munitions between North Korea and Russia.

Read: Seoul warns North Korea not to launch spy satellite and hints 2018 military deal could be suspended

South Korea’s National Intelligence Service, the country’s main spy agency, in a message sent to reporters on Tuesday said it had detected signs of North Korean preparations to send workers to Russia. The agency didn’t elaborate on what those signs were.

In a news conference in Seoul on Tuesday, South Korean Unification Minister Kim Yung Ho said his government is monitoring whether Russia is accepting more North Korean workers.

“The sending of North Korean workers to Russia would be a clear violation of U.N. Security Council resolutions,” he said. “As a permanent member of the Security Council, Russia has a responsibility to truthfully implement the council’s sanctions.”

North Korea last year hinted at an interest in sending construction workers to help rebuild Russia-backed separatist territories in the eastern region of Ukraine, an idea that was openly endorsed by senior Russian officials and diplomats, who foresee a cheap and hard-working workforce that could be thrown into the harsh conditions.

Read more: South Korea and members of the US-led UN command warn North Korea over its nuclear threat