Canada, along with France, Germany and the United States backed Britain and pledged on Thursday to work to disrupt "the hostile activities of foreign intelligence networks" and called on Russia to disclose its nerve agent programme.

Britain's security minister says Russian President Vladimir Putin bears ultimate responsibility for the Novichok nerve agent attack carried out in England.

"The fact that a nerve agent was used to do this is shocking. I don't want to describe the details but the clinical treatment was invasive, painful and depressing," Yulia Skripal said.