Britain's Defence Secretary has accused Russia of committing an attack on British soil following the death of a woman yesterday evening.

Dawn Sturgess, 44, died after she was exposed to Novichok on 30 June, just a few kilometres from where Sergei Skripal and his daughter Yulia were attacked with the same poison four months ago.

Speaking in the House of Commons, Gavin Williamson said: "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 actually condemning."

He also said the Ministry of Defence was working "incredibly closely" with the police on the investigation and the clear-up effort, adding 175 armed forces personnel were involved.

A senior British counter-terrorism officer has said that detectives were unable to say if the Novichok that two British people were exposed to was the same that struck down Mr Skripal, a former Russian double agent, and his daughter, as well as a police officer.

"This latest horrendous turn of events has only served to strengthen the resolve of our investigation team as we work to identify those responsible for this outrageous, reckless and barbaric act," Assistant Commissioner Neil Basu said.

"They are unable to say at this moment whether or not the nerve agent found in this incident is linked to the attack on Sergei and Yulia Skripal," he added.

Scotland Yard opened a murder investigation after Ms Sturgess died in hospital. Her partner Charlie Rowley, 45, is still in a critical condition after the couple fell ill in Amesbury, Wiltshire, on 30 June.

Assistant Commissioner Basu said the couple must have received a "high dose" of Novichok when they handled a vessel containing the nerve agent.

"Our focus and priority at this time is to indentify and locate any container that we believe may be the source of the contamination.

"In the four months since the Skripals and Nick Bailey were posioned, 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 had a high dose and our hypotheseis is that they must have handled a container that we are now seeking."

The investigation has spread to a third area with police seizing a car in Swindon.

Wiltshire Police said the vehicle was removed from an address in the town some 65km from Salisbury, where the Skripals were poisoned with Novichok.

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Ms Sturgess's family are being given support by specialist officers and have asked for privacy.

British Home Secretary Sajid Javid chaired a meeting of the government's Cobra emergencies committee.

Prime Minister Theresa May said she was "appalled and shocked", and sent her "thoughts and condolences" to the family.

In the House of Commons, she said: "I am sure the House will join me in sending our deepest condolences to the family and friends of Dawn Sturgess who passed away last night.

"The police and security services are working urgently to establish the full facts in now what is a murder investigation.

"I want to pay tribute to the dedication of staff at Salisbury District Hospital for their tireless work in responding to this appalling crime."

Dr Christine Blanshard, from Salisbury District Hospital where Ms Sturgess was treated, described her death as "desperately sad" and sent her condolences to the family.

She added: "The staff here at Salisbury District Hospital worked tirelessly to save Dawn.

"Our staff are talented, dedicated and professional and I know today they will be hurting too.

"They did everything they could."

A post-mortem examination will be scheduled to take place in due course.

The Kremlin has said that it was sorry to hear about the death of Ms Sturgess, but said that any suggestion that Russia was involved would be "quite absurd".

"We continue to be deeply worried by the continuing presence of these poisonous substances on British territory," Kremlin spokesman Dmitry Peskov told reporters when asked about the death of Ms Sturgess.

"We consider that it is a danger not only for the British, but for other Europeans," he said.

Russia, which is currently hosting the World Cup, has denied any involvement in the Skripal case and suggested the British security services had carried out the attack to stoke anti-Moscow hysteria.

Mr Peskov said the investigation and what was happening in the Salisbury area was a British issue that had nothing to do with an upcoming summit between President Vladimir Putin and US President Donald Trump.