The global chemical-weapons watchdog says it inspectors, using footage from sealed cameras, have verified one of two remaining sites declared by Syria.
The Organisation for the Prohibition of Chemical Weapons (OPCW), entrusted with overseeing the destruction of Syria's chemical-weapons stockpile, had already verified 21 out of 23 sites declared to the agency last month.
Two sites were considered too dangerous to reach because of the war.
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"The additional site inspected is in the region of Aleppo and was one of the two sites that could not be visited earlier due to safety and security reasons," the OPCW said in a statement on Thursday.
"As per the declaration by Syria, the site was confirmed as dismantled and long abandoned with the building showing extensive battle damage," it said.
Syria has proposed destroying its stockpile at a location outside the country because of ongoing fighting.
More than 100,000 people have been killed and some 2.2 million people have fled during the 2-1/2-year civil war.
The statement comes after the US ambassador to the UN, Samantha Power, suggested on Tuesday that the government of President Bashar al-Assad may not have disclosed its entire chemical weapons programme to the OPCW.
Under a Russian-American brokered deal, Syria agreed to destroy its entire stockpile of toxic nerve agents and munitions by mid-2014.
Syria declared 30 production, filling and storage facilities, eight mobile filling units and three chemical weapons-related facilities.
They contained about 1,300 tonnes of chemical weapons, mostly in the form of raw precursors, and 1,230 unfilled munitions.
A delegation of Syrian officials on Wednesday began talks in The Hague, where the OPCW is headquartered, to work out a detailed destruction plan by November 15.
The discussions are based on the assumption the weapons will be shipped overseas for destruction, a source involved in the talks told Reuters on Thursday.
Syria cannot afford to pay for the expensive destruction process itself and has appealed for significant foreign financing and logistical support.