"We stopped the ship after getting information on the weapons cargo," Torsten Luddkee, a shipping agent of Hamburg-based C.E.G Bulk Chartering, told the English-language Spiegel Online Friday.
Luddkee told the German magazine Web site the ship had been charted by an Odessa, Ukraine-based company called White Whale Shipping. "They declared to us as cargo mainly pumps and similar things. We would never have allowed weapons on board," he said.
Last week, at the port of Djibouti in the African Horn, an Iranian ship allegedly unloaded the weapons shipment and loaded it on to the German freighter called the Atlantic Cruiser, the Web site said.
Defectors from inside the Syrian government received information of the weapons and informed the German shipping company, the report said. They said the weapons were to assist President Bashar Assad's armed forces in its ongoing crackdown on anti-government protesters.
On Friday, the Atlantic Cruiser suddenly changed course and headed for the Turkish port of Iskender and then stopped about 50 miles southwest of the Syrian port of Tartus and began sailing in circles, Spiegel Online said.
The German Web site said it had learned the Cypriot port of Limassol refused to allow the ship to refuel after reporting its cargo as "weapons and munitions."
The Ukranian shipping company denies the cargo contains weapons and ammunition, and insists it be allowed to dock at the Syrian port of Tartus.
The sea route between Djibouti and Tartus is a known weapons smuggling route, Spiegel Online said. In January, a ship from Russia loaded with weapons was halted in Cyprus but permitted to continue its journey to Syria after the captain said he would head to a different port.