"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", Mr Basu said.
They were both left critically ill but recovered.
"The simple reality is that Russian Federation has committed an attack on British soil which has seen the death of a British citizen", Defense Secretary Gavin Williamson said when asked in parliament about the threat facing people in Britain after the death of Dawn Sturgess.
Russian Federation has repeatedly denied any involvement in the Skripal incident and offered to participate in a related investigation.
British Prime Minister Theresa May said she was "appalled and shocked" by the death of Dawn Sturgess, one of two people who fell ill last weekend in Amesbury, near the town of Salisbury.
Dawn Sturgess died after she was exposed to Novichok. Yulia said that the poisoning had turned her life "upside down" and that she and her father were "lucky to have survived this assassination attempt". Three men who also travelled in it show no signs of having been exposed to novichok.
Skripal was a Russian military intelligence officer, turned double agent for the UK.
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The police's "working hypothesis" is that the Amesbury poisoning and the Salisbury incident are linked, the home secretary said, but he called for the police to be given "time and space" to work.
Police in HAZMAT suits as they investigate the poisoning of two people in Salisbury.
Head of Britain's counter-terrorism policing, Assistant Commissioner Neil Basu, said it was "shocking and tragic news".
Glen told BBC radio the two may have handled a contaminated object due to their "habit of looking into bins" and police were trying to work out "how they came into contact with this nerve agent and when".
Rowley regularly scavenged for goods to fix and sell, leading to the possibility that he and Sturgess might have inadvertently found the container used to transport the Novichok.
"The simple reality is that Russian Federation has committed an attack on British soil which has seen the death of a British citizen", Williamson said.
Public Health England has emphasised that the overall risk to the public is low, but advised against picking up "any odd items such as needles, syringes or unusual containers".
They spent weeks in critical condition, but have both been discharged from Salisbury District Hospital, the same hospital where Sturgess died.