A British-registered vessel detained in Finland for two weeks after it was found to be carrying 69 Patriot missiles without proper documentation left the country Friday, a shipping official said.

"The (Thor Liberty) left this morning at around 4.00 am local time," a shipping agent representative told AFP, adding that it was bound for South Korea and China.

Thor Liberty had been at the southeastern Finnish port of Kotka since December 15, when the US-made surface-to-air missiles were found on board without the necessary authorisation to transit through Finnish territory.

A Finnish prosecutor last week charged the ship's Ukrainian captain and first mate with negligence for the improper loading of explosives, but lifted a travel ban on the officers.

The vessel was also found to be carrying 150 tons of nitroguanidine, a chemical used as an explosive propellant, stored in cardboard boxes rather than shipping containers.

Finnish officials launched an investigation into possible illegal transit of defence materiel but Berlin later said the missiles were from the German military and were destined for South Korea.

A German defence ministry spokesman said the weapons were being shipped as part of a "legal sale on the basis of an accord between two states at the government level" and that export authorisations were in order.

However a senior Finnish defence ministry official said Finland had not received a transit licence application from Germany.

The Finnish government on Wednesday approved the missiles' transit through Finnish territory to Seoul but customs officials said they were nonetheless continuing their probe.

"We will continue the investigation to try to find out what really happened, and whether anyone was negligent," the head of the Finnish customs anti-crime unit, Petri Lounatmaa, told AFP.