UN chief Antonio Guterres led praise at a solemn ceremony in The Hague for the work of the Organisation for the Prohibition of Chemical Weapons (OPCW) to mark the agency's 20th anniversary.
So far some 95 per cent of the world's declared stockpiles of such arms have been destroyed by the OPCW.
And its dangerous, painstaking work to implement the April 1997 Chemical Weapons Convention won it the Nobel Peace Prize in 2013.
"In the Middle East regions are breaking the norm against chemical weapons. The recent attack in Syria was a horrific reminder of this threat. There can be no impunity for these crimes," he stressed in a video-taped message to the ceremony.
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"For 20 years we have been allies in this cause. Now let us resolve to consign these diabolic weapons to the pages of history."
In an unprecedented step in November, the OPCW's executive council condemned Syria's use of toxic weapons -- its first public condemnation of any of the 192 members of the convention.
OPCW director general Ahmet Uzumcu acknowledged today that "our collective journey to banish forever the evil of chemical weapons has reached momentous landmarks."
But he warned that "in Syria the OPCW has faced its greatest test of commitment as well as resilience."
"Our work in Syria is not yet finished. It is of grave concern that we continue to see reports of the use of chemical weapons."
And with some victims in the audience, he paid tribute to those who have suffered most from such deadly weapons, first used on the battlefields of Ypres in World War I.
The victims "remind us of the human toll when morality is recklessly abandoned and universal norms callously breached," Uzumcu said.
"The work of the OPCW represents the most effective response to such cruelty; a ray of hope illuminating a dark shadow on our history.