The Pentagon said 15 percent of the main Syrian chemical weapons on board the U.S. cargo vessel MV Cape Ray have been destroyed.
The crew is working first to neutralize the raw material for sarin nerve gas, which makes up 581 metric tons of the chemical material on the ship.
Mustard gas accounts for the remaining 19 metric tons of chemical material on the Cape Ray.
The Pentagon has said it could take up to 60 days, depending on the weather and sea conditions, to destroy all the chemical toxins loaded on the ship.
The Cape Ray left Italy in early July and moved into international waters to begin the neutralization of the chemicals.
The 15 percent of the sarin toxin comes to about 88 metric tons.