WASHINGTON -- The Pentagon says the destruction of Syrian chemical weapons on board a U.S. cargo vessel has begun.

Army Col. Steve Warren says it will take about 60 days to destroy the approximately 600 metric tons of material. The Cape Ray left the Italian port of Gioia Tauro last Wednesday and is in international waters.

Last month Syria handed over to Western powers the 1,300 tons of chemical weapons it acknowledged possessing, completing a deal reached last year under threat of U.S. airstrikes.

The chemicals, including mustard gas and the raw materials for sarin nerve gas, are being neutralizd. The resulting waste will be taken to dumps equipped to handle hazardous materials. U.S. officials say no vapour or water runoff will be released into the atmosphere or the sea.