Britain's national security adviser has visited The Hague to rally support for his country's move to beef up the global chemical weapons watchdog.

Mark Sedwill met Thursday with several ambassadors from member states of the Organization for the Prohibition of Chemical Weapons. Britain needs 64 state parties to back its call to convene a special conference of the organization likely in late June.

London and its allies are understood to want the OPCW to begin apportioning blame for chemical attacks, in a move toward ending impunity for the use of poison gas and nerve agents.

Britain has called for a special OPCW conference "in response to shocking recent chemical attacks" including those in Salisbury, and in the Syrian civil war and by the Islamic State group in Iraq.