Finland wants to widen a probe into the illegal transit of 69 Patriot missiles through its territory aboard a regular merchant vessel, Finnish customs said Friday.

Two Ukrainians -- the ship's captain and the first mate -- remained in Finland and were subject to a travel ban amid the ongoing investigation.

"Next week... we will want to hear more suspects or persons of interest in the case. It is possible there may be others of interest," the head of the Finnish customs anti-crime unit, Petri Lounatmaa, told AFP.

The surface-to-air missiles, produced by US firm Raytheon, were discovered last week on the British-registered Thor Liberty docked in the southeastern Finnish port of Kotka and bound for the Chinese port city of Shanghai, according to Finnish police.

Finnish customs are investigating the case as one of illegal export of defence material.

Lounatmaa said customs and police investigators had "been in contact with several countries" and that the information gathered would help them "focus ... investigations in the right direction".

He declined to provide any details on the nature of the information received, noting only that some of it had come in the form of intelligence briefs.

More official information would be needed as evidence if the case goes to criminal proceedings, he said.

Last week, a German defence ministry spokesman said the missiles came from the German military and were destined for South Korea, not China.

He said it was 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 defense ministry official said Finland had not received any transit license application for the missiles from Germany.

On Monday, Finnish transport safety officials cleared the Thor Liberty to leave Finland, after the missiles and most of the cargo of 150 tons of explosives had been unloaded from the vessel.

However the vessel remained grounded by the travel ban on its first officers.