Greece said Monday it would hold as unsafe a Sierra Leone-flagged cargo ship that was seized last week laden with arms and ammunition possibly bound for war-ravaged Syria.

"The ship does not meet safety standards and for this reason it will be held," Merchant Marine Minister Miltiades Varvitsiotis said, in statements reported by the state-run Athens News Agency (ANA).

"We are obliged to keep the ship for as long as it takes," he added. 'We're here to find out what the situation is with the suspicious ship and cargo."

ANA reported that the vessel, intercepted near the Greek island of Symi with some 20,000 Kalashnikov assault rifles on board, had set sail from Ukraine and was bound for the Turkish port of Iskenderun, according to its captain.

But the Syrian port of Tartus and Tripoli in Libya were also declared as destination ports to maritime traffic systems, ANA reported.

"From the documents and statements of the crew, the destination of these arms and ammunition is not clear," said coastguard chief Dimitris Bantias.

"According to the documentation and the crew statements, which are conflicting until this point, the ship was headed for Mediterranean countries which are in a state of war," the minister said.

"The UN prohibits the shipment of arms and bullets to such countries."

The cargo ship, Nour M, was intercepted by the Greek coastguard on Friday and taken to the island of Rhodes where its Turkish captain and seven Turkish and Indian crew members were placed under arrest.

A search of the containers on board uncovered ammunition "of various calibres", the minister said, while coastguard officials said the ship also carries firearms, according to cargo documents.

"We have not managed to open all the boxes yet, but it carries bullets and arms," Varvitsiotis said.

The Nour M is also believed to have been used in the past for drug trafficking, ANA said.