French President Emmanuel Macron and British Prime Minister Theresa May yesterday urged the world to keep up the fight against chemical weapons on the anniversary of an international convention banning their use.

"On the 21st anniversary of the Chemical Weapons Convention, and following Douma and Salisbury, Theresa May and I call with one voice for the world to join us in upholding the vital global prohibition on chemical weapons use," Macron tweeted in English and French, referring to recent chemical attacks in Syria and Britain.

May's office tweeted a similar statement, also in both languages, saying "we should never go back" on ending the production, stockpiling and use "of these terrible weapons."

Chemical weapons, such as mustard gas, were first used on the battlefields of World War I and also in 1988 by late Iraqi dictator Saddam Hussein against civilians in Halabja, Iraq.

The Chemical Weapons Convention (CWC) convention, which oversees the destruction of such arms, came into effect on April 29, 1997.