SEOUL, Jan. 5 (Yonhap) -- South Korea is seeking U.S. cooperation to ensure safe shipment of missiles that were detained in Finland, government sources said Thursday.

One source said a British-registered ship, named Thor Liberty, has been authorized to leave the port in Kotka, southern Finland.

The ship, carrying 69 surface-to-air missiles from Germany to South Korea, was impounded there last month.

It sought safe harbor in Finland to avoid a typhoon. Local authorities, however, discovered that the vessel did not have proper transit documents for its shipment of missiles and other explosives, since it was not initially scheduled to make a stop there.

With the ship about to depart for South Korea after clearing administrative issues, safety concerns have emerged, the source said.

"Foreign news wires have reported that the ship has Patriot missiles, and it is possible that pirates and international terrorists could try to seize the ship," the source said. "The government has asked the U.S. to use their intelligence assets to help ensure safe travel of this ship."

The source said the U.S. is operating satellites monitoring situations in the Pacific Ocean and has installed long-range sea surveillance radars in Hawaii and other places.

Another source said the United States will begin real-time monitoring of suspected pirate ships around the planned route for Thor Liberty once the ship leaves Finland.

"I understand the U.S. also plans to dispatch their naval destroyer from nearby once a pirate ship or a suspected one moves closer to the cargo ship," the second source said.

The South Korean Navy's Cheonghae Unit operates in the Gulf of Aden on an anti-piracy mission, but it will not be deployed for Thor Liberty because of the distance, the source added.

An official with the Defense Acquisition Program Administration (DAPA), the state arms procurement agency, declined to disclose the exact date of Thor Liberty's departure for security reasons. He said the travel from Finland would take about 40 days.