The world's chemical weapons watchdog on Wednesday agreed to ban Soviet-era Novichoks, the type of nerve agents used in the attempt to kill a Russian ex-spy in the English city of Salisbury.

Applause broke out after diplomats from the body's 193 member states agreed to update the list of banned substances in the Chemical Weapons Convention for the first time since its entry into force in 1997.

"Today we live in an important moment," Fernando Arias, the head of the Organisation for the Prohibition of Chemical Weapons, told the watchdog's annual meeting in The Hague.

"This is the first time in its history that the Chemical Weapons Convention's annex on chemicals has been updated," he said, adding that it "demonstrates the adaptability of the convention to changing threats."

The US State Department said its representative at the meeting, Tom DiNanno, "applauds (the) consensus decision to add Novichoks" to the banned list.

Western nations said Russian intelligence was behind the March 2018 attack that left former Russian double agent Sergei Skripal and his daughter critically ill, and said Novichok was used to poison them.

The attack also led to the death of a British woman who came into contact with the nerve agent, as well as injuring several others including a policeman.

Moscow denied all involvement and insists it has destroyed all of its chemical weapons.

Canada, the Netherlands and the United States put forward the proposal in 2018 to ban the Novichoks, which were developed by the Soviet Union's chemical weapons programme.

Russia then put forward its own proposal to ban several Novichok-type chemicals that it said the United States had previously developed.

The two sides wrangled for months over which substances should be included before finally reaching a consensus on both the western and the Russian proposals, diplomats said.

The agreement was a rare moment of compromise during an increasingly tense meeting which has seen Russia oppose the OPCW's new budget as it will fund a new team that will assign blame for chemical attacks in Syria.

Copyright Agence France-Presse, 2019