8 March 2018
The attempted murder of ex-Russian spy Sergei Skripal and his daughter, Yulia, using a nerve agent was a "brazen and reckless attack", Amber Rudd has said.
Both Mr Skripal and his daughter are still critically ill after being found collapsed on a bench in Salisbury city centre on Sunday.
Counter-terrorism officers are working to find the origin of the nerve agent.
A police officer, who was in intensive care, is now "stable and conscious", Wiltshire's chief constable said.
Addressing the House of Commons, the home secretary said the attack was "attempted murder in the most cruel and public way".
Ms Rudd told MPs it was an "outrageous crime", adding that the government would "act without hesitation as the facts become clearer".
She refused to speculate on whether the Russian state might have been involved in the attack, saying the police investigation should be based on "facts, not rumour".
However, she said the government was committed to bringing the perpetrators to justice "whoever they are and wherever they may be".
A Downing Street spokesman described the attack as an "appalling and reckless crime" and said those responsible would face a "robust" response.
Earlier, Ms Rudd said the nerve agent used in the poisoning was "very rare".
Police said government scientists had identified the nerve agent used, but would not make that information public at this stage.
The source familiar with the investigation told the BBC it was likely to be rarer than the Sarin gas thought to have been used in Syria and in an attack on the Tokyo subway in 1995.
And it was said not to be VX - the nerve agent used to kill the half brother of the North Korean leader Kim Jong-un in Malaysia last year.