SEOUL, Oct. 2 (Yonhap) -- South Korea said Tuesday it will swiftly complete the investigation into a detained Russian cargo ship suspected of having ties with North Korea in consideration of not only U.S.-led sanctions but also bilateral relations with Moscow.

South Korea has banned the Sevastopol from leaving a Busan port. On Monday, Russia summoned Seoul's ambassador to Moscow, Woo Yoon-keun, in protest against the "illegal" seizure and demanded its immediate release.

It's one of six Russian-flagged vessels blacklisted by the U.S. government in August as part of efforts to foil North Korea's clandestine trade that breaches the U.N. Security Council resolutions.

"The government has been conducting an investigation with regard to the Sevastopol," the foreign ministry's spokesman Noh Kyu-duk said at a press briefing. "The government is in the speedy process of handling it."

He cited the dilemma of balancing South Korea's relations with Russia and its commitment to the faithful implementation of U.N. sanctions.

He also raised the possibility of damage to South Korean firms from the U.S. restrictions.

The Sevastopol arrived at the local port for "repair purposes" days before the announcement of the U.S. measure.

Source: Yonhap News Agency