The destruction of "primary" chemicals - mustard gas and the components for making Sarin and VX - had originally been foreseen completed by the end of March but the civil war, bad weather and bureaucracy have slowed it.
Nonetheless, Ahmet Uzumcu, head of the Organisation For The Prohibition Of Chemical Weapons, told reporters in Rome he was confident all the chemicals could be destroyed by the end of June, the deadline set only for the destruction of the less dangerous "commodity" chemicals.
He said: "I am still confident we can meet this deadline of the end of June. We will do our best to meet this deadline."
Mr Uzumcu said more than 16 tonnes of the total of 560 tonnes of the "primary" chemicals had so far been shifted to a Danish vessel in the Syrian port Latakia.