"We hope that by the end of January, the destruction on the American ship could start," the director general of the Hague-based Organisation for the Prohibition of Chemical Weapons (OPCW), Ahmet Uzumcu, told AFP.
The Syrian weapons are to be destroyed aboard the US Navy's MV Cape Ray, a 200-metre (650-foot) cargo ship equipped.
"Much will depend in fact on the security situation and unfortunately the security situation has deteriorated over the past weeks. Some roads were not accessible," Uzumcu said.
Uzumcu was speaking in the Norwegian capital Oslo, ahead of formally receiving the Nobel Peace Prize which was awarded to the OPCW in October.
The OPCW has spent years trying to rid the world of chemical weapons in relative obscurity before being thrust into the global limelight by the Syrian crisis.
To be shipped out of the country, Syria's chemical arms must be transported through a war zone to the Mediterranean port of Latakia.
"There could be some slight delays but I'm not that worried about delays. For me what's important is this operation takes place in the safest and most secure manner," Uzumcu said.
A roadmap adopted last month by the OPCW to rid Syria of its chemical stockpile says "priority" weapons must be removed from the country by December 31.
"As to the Category Two chemical weapons which will be destroyed in commercial destruction plants, we hope that this operation could begin sometime in February," Uzumcu said.