Defence Secretary Gavin Williamson has accused Russia of committing “an attack on British soil” over the death of Dawn Sturgess from Novichok poisoning.
Ms Sturgess, 44, died and her partner Charlie Rowley, 45, is in a critical condition after the couple fell ill in Amesbury, Wiltshire, on 30 June.
Investigators said their main line of inquiry is whether the poisoning is linked to the case of Sergei and Yulia Skripal, who were left critically ill in March. They both recovered.
Yesterday Mr Williamson went a step further in pointing the finger at Moscow.
He told MPs: “The simple reality is that Russia has committed an attack on British soil which has seen the death of a British citizen. That is something that I think the world will unite with us in condemning.”
He was backed by Salisbury MP John Glen, who also said: “The poisoning of Dawn Sturgess and Charlie Rowley is very likely the result of picking up a discarded container from the original attack, at a site not previously connected to the Skripal case.
“The only way the current poisoning could likely have been averted would have been to conduct a fingertip search of every square inch of South Wiltshire – a logistical impossibility, especially when there was no way for the police to know that an object from the original incident had been discarded like this.
“There is always a temptation in these circumstances to look to blame the government, or the police, or the local authority. But we must not lose sight of the fact that responsibility for the fact that a military-grade nerve agent was used in Salisbury and South Wiltshire rests with Vladimir Putin’s Kremlin alone.”
The Ministry of Defence is working with the police on the investigation and the clear-up effort, with about 175 armed forces personnel involved.
Metropolitan Police Assistant Commissioner Neil Basu, who oversees counter-terrorism policing, said: “Our focus and priority at this time is to identify and locate any container we believe may be the source of the contamination.
“In the four months since the Skripals and [police officer] Nick Bailey were poisoned, no other people besides Dawn and Charlie have presented with symptoms. But their reaction was so severe it resulted in Dawn’s death and Charlie being critically ill.
“This means they must have got a high dose and our hypothesis is that they must have handled a container that we are now seeking.”
Public Health England has emphasised that the overall risk to the public is low, but advised against picking up “any strange items such as needles, syringes or unusual containers”.
Kremlin spokesman Dmitry Peskov told reporters that linking Russia to the poisoning would be “absurd”.