Around 180 military personnel have been drafted into Salisbury, removing objects and vehicles, including ambulances that may have been contaminated.
Officials said 21 people in Salisbury had received medical treatment as a result of the nerve agent, including a police officer who was in serious condition.
They remained in critical condition in a hospital Friday, poisoned with what authorities say is a nerve agent.
Defence Secretary Gavin Williamson said: "Our armed forces have stepped up to support the police in their investigation in Salisbury, building on the vital expertise and information already provided by our world-renowned scientists from the Defence Science and Technology Laboratory at Porton Down".
"In terms of further options, that will have to wait until we're absolutely clear what the consequences could be, and what the actual source of this nerve agent has been", Rudd said after visiting Salisbury and seeing the area around the bench where Skripal was found, now covered by a police forensics tent.
During the attempted poisoning of former Russian intelligence officer Sergei Skripal in the British city of Salisbury, injured 20 people, including the daughter of Yulia Skripal and Sergeant nick Bailey.
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".
Home Secretary Amber Rudd is chairing an emergency meeting of the Government's Cobra committee following the nerve agent attack on ex-Russian spy Sergei Skripal and his daughter in Salisbury.
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.
Meanwhile, Russia's foreign minister expressed resentment at suggestions Moscow was behind the attack and said the Kremlin was "ready to consider" lending a hand in any investigation, "whether it's [about] poisoning of some British subjects, whether it's rumors about interference in the US election campaign".
Police have cordoned off the graves of his wife and son, who died since his move to England, suggesting that the bodies could be disinterred for examination.
The pair are critically ill after being attacked with an undisclosed nerve agent.
"But in order to conduct such cases, it is necessary not to immediately run out on TV screens with unfounded allegations", Russian Foreign Minister Sergey Lavrov was quoted as saying by Russian state news agency Tass.
After serving four years in prison in Russia for spying for Britain's espionage service, MI6, Skripal was one of four Russian double agents exchanged for 10 Russians expelled from the United States, including Manhattan socialite Anna Chapman.
The U.K. has vowed to take strong action against whoever was responsible for the "brazen and reckless" attack.
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.
Russian officials deny the Kremlin had anything to do with the assassination attempt. "If you really need help from Russian Federation, then we will be ready to consider such a possibility, if we do have relevant data", he said, speaking in Addis Ababa, Ethiopia.
More: Ex-Russian spy attacked with unknown nerve agent.
A British public inquiry said Litvinenko's murder had probably been approved by Putin and carried out by two Russians, Dmitry Kovtun and Andrei Lugovoy.
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