The crew of a Danish weapons ship have been kidnapped by pirates in the Gulf of Aden off Oman, but in an unusual departure from normal practice, the vessel was not seized, a report said Thursday.

Sources told the TradeWinds shipping publication that the 2,000-tonne ship, The Leopard, was carrying "sensitive" cargo, believed to include weapons.

Vessels operated by the Leopard's Danish operator, Shipcraft, routinely carried nuclear items, although none were believed to have been on board this vessel, it said.

The six crew -- two Danes including the captain, and four Filipinos -- had been taken to a seized Taiwanese fishing vessel being operated as a mothership, the report added.

The ship had meanwhile been located and searched by the Turkish navy and no trace of any pirates or pirate skiffs had been found.

It was believed that the pirates may have already made contact with the ship's operator.

Late Wednesday, Shipcraft chief Claus Bech said the Leopard, had been attacked but that he had not received any news since.

Bech said the ship was "equipped with barbed wire and steel plates that protect its windows and doors in order to withstand pirate attacks and to allow the crew to regain a secure cabin."

Somali pirates, targeting one of the world's busiest maritime trade routes, have made tens of millions of dollars in ransom by seizing ships in the Indian Ocean and the Gulf of Aden.

In 2009, Somali hijackers attacked more than 130 merchant ships off Somalia, a rise of more than 200 percent on 2007, according to the International Maritime Bureau's Piracy Reporting Centre in Kuala Lumpur.