Safety concerns have prevented inspectors from a global chemical weapons watchdog from reaching two of the 23 sites declared by Syria as part of an agreement to destroy its toxic arsenal, the organization said on Monday.
The Organisation for Prohibition of Chemical Weapons (OPCW) had verified 21 sites up to October 27, the deadline agreed as part of Syria's destruction program.
"The two remaining sites have not been visited due to security reasons," the OPCW, which won the Nobel Peace prize this month, said in a statement.
Visiting the sites has posed serious dangers for the inspectors with fighting continuing to rage in a 2-1/2 year civil war that has killed more than 100,000 people.
"Efforts by the Joint Mission (with the UN) to ensure the conditions necessary for safe access to those sites will continue," the statement said.
The location of the remaining sites was not provided by the OPCW, but an official speaking on condition of anonymity said "one is empty and the other is also otherwise not that important."
By another deadline next Friday, Syria must have rendered unusable all production and chemical weapons filling facilities. By mid-2014 it must have destroyed its entire stockpile of chemical weapons.
Syria has not revealed the exact size of its arsenal, but experts believe it includes roughly 1,000 metric tons of nerve agents, including sarin, mustard and VX.
Under a Russian-American brokered deal, Damascus agreed to destroy all its chemical weapons after Washington threatened to use force in response to the killing of hundreds of people in a poison gas attack on August 2.