THE HAGUE - All Syria's precursor chemicals that could be used to make deadly sarin gas have been destroyed on board a US Navy ship on the Mediterranean Sea, the world's chemical watchdog said on Wednesday.

"All 581 metric tonnes of a precursor chemical for sarin gas that were removed from Syria and trans-loaded onto the US vessel Cape Ray, have been destroyed with neutralisation technology on board the ship," the Organisation for the Prohibition of Chemical Weapons said, confirming an Pentagon report on Tuesday.

The precursor chemical, called methylphosphonyl difluoride, or DF, was neutralised with two field hydrolysis systems installed on the Cape Ray, the Hague-based watchdog said.

"The Cape Ray has now begun operations to neutralise 19.8 metric tonnes of sulfur mustard, a blistering agent, which is the only Syrian chemical that remain on the ship," the OPCW said. The ship was sailing "in international waters of the Mediterranean Sea", it added. The effluent from the hydrolysis process will be taken off the ship and destroyed at land-based facilities in Germany and Finland. Last week the OPCW said almost three quarters of Syria's entire chemical arsenal had now been destroyed.

The Syrian regime of President Bashar al-Assad agreed to an international plan last year to destroy its chemical weapons stockpile after a global outcry over chemical attacks in a Damascus suburb last year that may have killed as many as 1,400 people.