British registered cargo ship MS Thor Liberty is docked at Mussalo harbour in Kotka, about 120 kilometres (75 miles) from Helsinki December 21, 2011. Finnish customs found 69 surface-to-air Patriot missiles in the ship.[Photo/Agencies]

HELSINKI - Finnish authorities have confiscated 69 Patriot missiles found on a ship and arrested its Ukrainian captain and chief officer on suspicion of trying to transport the missiles via Finland without permission.

The surface-to-air missiles were found on Wednesday when authorities searched the cargo ship Thor Liberty in Kotka, southern Finland. They also discovered 150 tonnes of explosive material called nitroguanidine, which was not stowed properly.

"We arrested the captain and chief officer yesterday," said Petri Lounatmaa, head of investigation at the custom office's economic crime division.  

He declined to comment on what the suspects have said, or on the destination of the missiles.  

Finnish public broadcaster YLE reported the missiles had been sold by Germany to South Korea.

Finland requires those seeking to transport defence material via Finland to seek permission. In the past six years there have been 20 cases of defence material being transported without the required documentation with the latest incident appearing to be one of the largest consignments.

"I don't remember a case of this scale," Lounatmaa said.

He said requests for information had been sent to several countries and said the length of the investigation would depend on how quickly they could get replies from abroad.

The ship was sailing under an Isle of Man flag and had stopped to load anchor cables on board.  

The vessel's owner, Thorco Shipping, was not immediately available for comment.