"This is shocking and tragic news", Neil Basu, of the UK's counterterrorism agency, said. Mr Rowley, 45, remains in a critical condition.
The statement added that blame on the Russian government for either the Skripal or Sturgess poisonings are "quite absurd.we continue to be deeply anxious by the continuing presence of these poisonous substances on British territory".
The Kremlin has denied, as it did after attack on Skripal, any involvement with poisoning of Rowley and Sturgess, which it considers "deeply troubling", and called on British authorities not to incur "dirty political games" by relating Poisoning with case of Skripal.
The death of Sturgess is now being investigated as a murder.
A post-mortem examination of Ms Sturgess, from Durrington, is due to take place and her family has been informed, police said.
Britain "understands that direct dialogue between the two superpowers is capable of reducing the level of confrontation, gradually raising the level of trust between our countries, and destroying the lies fabricated against Russia", Zheleznyak said in July 9 comments released by his party.
Skripal was a former Russian spy who became a double-agent for the United Kingdom intelligence services.
The same nerve agent was used to poison former Russian spy Sergei Skripal and his daughter Yulia in March. "I think someone from counter-terrorism needs to come here and tell us what they know", he said.
"The possibility that the two investigations might be linked is clearly a key line of inquiry for police".
The 44-year-old was found unconscious at a residential address along with her partner Charlie Rowley, on June 30. It came as Scotland Yard said it "cannot offer any guarantees" that others won't be poisoned and revealed a red van travelled in by Mr Rowley on the day he fell ill has been sent to Porton Down for testing.
Christine Blanshard, medical director at Salisbury District Hospital, where Sturgess and Rowley were being treated and where the Skripals were hospitalised, told the Daily Telegraph that staff had "worked tirelessly to save Dawn".
Last week, the Chief Medical Officer for England said that the risk to the wider public remains low but that people in the local area should not pick up any odd items such as needles, syringes or unusual containers, given the source of the contamination has not yet been found. "However, it is important that the investigation is led by the evidence available and the facts alone", the Met said.