The Russian Foreign Ministry has summoned South Korea’s ambassador in Moscow and demanded that Seoul allow a Russian vessel to leave South Korea’s port of Busan.

The ministry said in a statement that it summoned Ambassador Woo Yoon-keun on Monday and called for Seoul's immediate release of the vessel named "Sevastopol" that has been illegally held at the port.

The cargo ship, which belongs to Russian shipping firm Gudzon, is reportedly one of six Russian-flagged vessels targeted by U.S. sanctions in August for alleged breaches of United Nations restrictions on North Korea. 

Washington accused the vessels and two Russian shipping companies of involvement in the transfer of refined petroleum products to North Korean vessels.