A British-flagged cargo ship has been impounded by Finnish authorities after 160 tonnes of explosives and 69 surface-to-air missiles were found on board.

The Thor Liberty was on its way to Shanghai, China, after setting sail from the German port of Emden on 13 December. The British-registered ship, owned by a Danish firm, Thorco, docked two days later in Kotka, Finland, to pick up a cargo of anchor chains.

The missiles, produced by the US firm Raytheon, were discovered after a search of the vessel by customs officials. Petri Lounatmaa, a Finnish customs spokesman, said investigators did not yet know the origin of the Patriot missiles or who was supposed to receive them.

"We have impounded the explosives and missiles and asked the Defence Ministry to transport and store them," Mr Lounatmaa said.

"At this stage we don't know where it [the cargo] was loaded on the ship or if the Thor Liberty planned a drop before its port of destination in China." Mr Lounatmaa said customs officials and police have launched a joint investigation into a possible breach of Finnish export and weapons-trading laws. "We have started questioning the crew," Mr Lounatmaa said. "As the investigation continues decisions will be made about possible arrests."

Mr Lounatmaa said that there were about 32 crew members on board the vessel and that questioning them could continue well into Friday. Detective Superintendent Timo Virtanen, of the National Bureau of Investigation, said dock workers found the explosives – picric acid – stored on open pallets instead of in closed containers. They alerted inspectors, who found the missiles in containers with markings that indicated they were holding fireworks.

The Finnish Interior Minister Paivi Rasanen said she had not heard of a similar case. "Of course, there are legal transports of weapons or defence material [through Finland], but in this case the cargo was marked as containing fireworks," she told Finland's YLE TV.

Belfast Telegraph