About 180 military personnel from the Royal Marines, the Royal Air Force (RAF) and other military establishments were deployed in Salisbury in the south-west England, where the former Russian spy Sergei Skripal, 66 and his daughter Yulia, 33 were found collapsed after being poisoned on Sunday afternoon.
Skripal and Yulia remain in a serious condition along with a police officer who came in contact with the same substance.
UK defence secretary Gavin Williamson said the military had stepped up to "assist with this crucial inquiry" as speculation surrounding Russia's involvement in the attack continued.
We have the right people with the right skills to assist with this crucial inquiry. This is a dreadful incident and my thoughts remain with the victims and their families, he said.
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For the police officer (Detective Sergeant Nick Bailey), it is still serious but we understand he is conversing and engaging, she said.
At the moment our priority is going to be the incident. In terms of further options, that will have to wait until were absolutely clear what the consequences could be and what the actual source of this nerve agent has been, she added.
According to reports, Bailey was poisoned at the Skripal family home in Salisbury, indicating that the nerve agent was administered there.
Yesterday, the investigation had widened as police sealed off the graves of Skripal's wife, Liudmila, and his son, Alexander, and said 21 people had been treated as a result of the incident.
Rudd has refused to speculate on whether the Russian state might have been involved in the attack, saying the police investigation should be based on "facts, not rumour.
Russian Foreign Minister Sergei Lavrov has categorically denied any Kremlin involvement, dismissing it as baseless "propaganda".
But the attempted murder of Skripal has drawn comparisons to the 2006 assassination of another Russian spy Alexander Litvinenko, who ingested the rare and highly radioactive polonium 210 in London.