LONDON — International chemical weapons inspectors reported further progress on Thursday in eliminating Syria’s stockpile, saying they had verified the destruction of 22 of the 23 sites that the Syrian government declared had been used for the production and mixing of the banned munitions.

The inspectors, deployed in a joint operation by the United Nations and the Organization for the Prohibition of Chemical Weapons, said they had used special cameras to determine that the 22nd site, in the northern Aleppo region, had been destroyed. The cameras were operated by Syrian personnel working under the inspectors’ supervision, eliminating any possibility of mistake or deception, they said.

“The cameras had been rendered tamper-proof and equipped in such a way that we knew at all times where they were,” a spokesman for the Hague-based organization, Christian Chartier, said in an email. “Thanks to these devices, the footage could not be edited. It was then checked against satellite imagery and cross-referenced with other data.”

The cameras showed the site had long been abandoned and damaged by fighting in the civil war, the organization said in a statement on its website.