Threats and allegations about the possible use of nuclear, chemical and biological weapons have been traded since the war in Ukraine began in February, but with no evidence they have been deployed.
Russia's invasion of Ukraine has increased the threat of the use of weapons of mass destruction including chemical munitions, according to the head of the world's toxic arms watchdog.
The Organization for the Prohibition of Chemical Weapons (OPCW) summit opened in The Hague on Monday with a stark warning.
"It [the war] has exacerbated existing tensions to a point where the unity of the international community on common global challenges related to international security and peace cannot be presumed," said Fernando Arias, OPCW director general.
Battlefield setbacks rekindle fears
Russia and Ukraine have accused each other of the possible use of chemical and biological weapons since the start of the conflict in Ukraine last February.
Moscow claims that Kyiv tried to develop a biological weapons program together with the United States.
But neither has presented credible evidence of these accusations.
The setbacks suffered by the Russian Army on the battlefield have rekindled fears of Russia's use of weapons of mass destruction.
Last week, Russia test-fired its new nuclear intercontinental ballistic missile just days after the Kremlin insisted that using nuclear weapons in Ukraine was out of the question.