Authorities in Finland have reportedly confiscated missiles found aboard a Manx-registered ship, saying the vessel didn't have permission to transport them.
The Thor Liberty was detained in Kotka, in the south of the country, after police found 69 patriot missiles and more than 150 tonnes of explosives.
The Manx ship registry has said the Finns were concerned some of the explosive chemicals hadn't been properly secured.
However, reports now say police have arrested the Thor Liberty's Ukrainian captain and chief officer, on suspicion of trying to transport defence material via Finland without permission.
China has denied any link to the missiles, saying the weapons were destined for South Korea.
The ship was sailing under an Isle of Man flag and had stopped to load anchor cables on board.
Petri Lounatmaa, head of investigation at the Finnish customs office economic crime division, says in recent years there have been a number of such cases, but the latest incident involves one of the largest ever consignments.
He says prosecutors have sent requests for information to several countries and the investigation is continuing.
The missiles had come from Germany, and the authorities say they were legal and authorised, and bound for South Korea.