The head of the world's chemical weapons watchdog on Thursday will announce to Italy's parliament the port through which a shipment of arms from Syria slated for destruction will transit, the foreign ministry said.

The ministry said in a statement on Monday that Ahmet Uzumcu, head of the Organisation for the Prohibition of Chemical Weapons (OPCW), will make the announcement.

It also said that Rome will host a UN-led conference on humanitarian aid for Syria on February 3, after the start of the Geneva II peace talks on January 22.

"The choice of port is made on the basis of the technical requirements that have been asked of us," it said, following opposition from local officials in several of the possible ports named in the press so far.

"The operation should take place by the end of the month with inspectors from the OPCW," it said, adding that Uzumcu would meet with Foreign Minister Emma Bonino ahead of his address to parliament.

Syria's most dangerous chemicals were meant to have been moved out of the country by December 31.

Under a UN-backed plan, all of Syria's declared 1,290 tonne arsenal should be destroyed by June 30.

But the worsening conflict has caused holdups.

Containers of Class A chemicals from Syria's arsenal were put on a Danish vessel in Latakia last week, which is now being guarded at sea by an international fleet.

After more chemicals have been loaded, the consignment will be taken to Italy to be transferred to a US Navy vessel for destruction to start.

The American ship, the MV Cape Ray, outfitted with hydrolysis equipment designed to neutralise the lethal chemical agents, is due to set off from the United States within days, according to the Pentagon.

"The Cape Ray is scheduled to return to port tomorrow for some final outfitting and it will be prepared to depart late this week or early next week," spokesman Colonel Steven Warren told reporters in Washington.

The cargo ship is currently undergoing its final sea trials before a two-week transit to Italy, he added.