Counterterrorism police requested the deployment of military personnel to help "remove a number of vehicles and objects" in Salisbury, London's Metropolitan Police said.
Police say their deaths are part of the investigation into the poisoning of Mr Skripal, 66, and his daughter Yulia, 33, who were found slumped on a park bench in Salisbury on Sunday evening. "I understand it's still serious, although he's still conversing and engaging", said Ms Rudd.
Russian Federation was not involved in the attempted murder of an ex-spy and is willing to help with a United Kingdom inquiry, the country's foreign minister has said.
Only DS Bailey and the Skripals, who are both critically ill, remain in hospital.
Rudd said more than 250 counter terrorism police, from eight out of Britain's 11 specialist units, were involved in the investigation, which was proceeding with "speed and professionalism".
Police identified the officer as Detective Sgt. Nick Bailey, and said he was conscious and talking with visitors.
Investigators are said to be probing whether Yulia could have brought the toxin with her from Russian Federation as a present from friends for her father.
Russian Foreign Minister Sergei Lavrov said Russia would consider helping in the death of Sergei Skripal if asked.
The grave of Skripal's wife, Liudmila, who died in 2012 from cancer, was also sealed off.
Suspicion is mounting that Russian Federation attempted to kill the former intelligence officer and his daughter as an act of revenge against Mr Skripal, who was convicted in 2006 of selling state secrets to MI6.
Police say they know the nerve agent used in the attack, but have declined to say what it was or how they suspect it was administered.
Britain was to hold a second meeting of its national emergencies committee on Saturday in response to a nerve agent attack on a Russian former spy.
On Friday, Russian Foreign Ministry Sergey Lavrov said Russia was ready to assist "any investigation" but that it was "not necessary to hurl unfounded accusations on TV".
Former London Police Chief Ian Blair said Friday that the police officer who is seriously ill had visited Skripal's house - suggesting that the nerve agent was delivered there.
Russian Federation is fighting a new Cold War against Britain which people need to be aware of, an MP has warned.
Meanwhile Salisbury's MP John Glen, also a Government minister, attempted to reassure his constituents that a "whole range of tools are at our disposal" once it is established who was behind the incident.
A British public inquiry found Russia was responsible for Litvinenko's killing, and Russian President Vladimir Putin probably approved it.
Local convenience store manager Ebru Ozturk, who saw Skripal at his shop just days before the incident, told CNN that he was a "kind customer" who would usually come in once a week and buy Polish-smoked bacon and scratch-and-win lottery cards.
In response to questions over Russia's possible involvement, May has said that "if action needs to be taken then the government will do that".
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