Sigrid Kaag, in an interview with AFP yesterday, was confident however that a mid-2014 deadline for the regime's entire arsenal to be destroyed would be met.
Syria, Kaag said, was continuing to display "constructive cooperation" despite missing several deadlines to ship chemical material out of the country.
"Some delays have been encountered, but they have not been insurmountable and we remain confident that the deadline of 30th June 2014 will be met," she said.
"But yes, there is constructive cooperation at the political and at the technical level."
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The entire arsenal is scheduled to be destroyed by June 2014 in a mission overseen by the joint UN-Organisation for the Prohibition of Chemical Weapons team that Kaag heads.
On Monday, a third shipment of chemical material left Syria to be destroyed overseas.
"A significant effort is needed to ensure the chemicals that still remain in Syria are removed -- in accordance with a concrete schedule and without further delay," Uzumcu warned earlier this week.
US President Barack Obama yesterday put the onus on Syria ally Russia to make sure the deadlines are met.
"Syria must meet its commitments and Russia has a responsibility to ensure that Syria complies," Obama said at a Washington press conference with French President Francois Hollande.