The removal and destruction of the most dangerous agents in Syria's chemical arsenal may not be completed until the end of June because of logistical and security problems, the head of the UN chemicals watchdog said today.

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 that all the chemicals could be destroyed by the end of June, the deadline set for only the destruction the less dangerous "commodity" chemicals.

"I am still confident that we can meet this deadline of the end of June ... We will do our best to meet this deadline," he said.

Uzumcu said that 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, conceding: "The quantity of the first movement is not that high."

The ship is now waiting in international waters offshore for more shipments.

Uzumcu is in Italy to address parliament about the transfer of the primary agents at an Italian port from the Danish vessel to an American one, where they will be destroyed at sea. The Calabrian port of Gioia Tauro has been chosen for the chemical transfer, an Italian government source said.