The British Home Office accused Russia of "reckless and callous" behavior and demanded that Moscow provide details about the nerve-agent attack on a Russian former double agent and his daughter in March after two British citizens were poisoned with the same substance last week.
Britain blamed Russian Federation for the March attack, but Moscow officials denied any involvement.
Wiltshire residents have been told to expect investigators in hazardous material suits to descend on the scenes, while other sites the couple were known to have visited before being taken ill are behind cordons.
Security Minister Ben Wallace told BBC News Thursday that the couple is likely just a victim of the consequences of the earlier attack and that they were not directly targeted.
It is unclear whether there is any connection between the Skripal attack and the current incident.
Police officer being tested at hospital for possible contact with nerve agent in the United Kingdom; Kitty Logan reports.
"He started feeling really hot and sweaty.so he went and had a shower, he was in his bedroom for a while and then he came out and felt a bit weird and started acting all amusing", said Hobson. "The offer is there. We inform the British side about this regularly, several times a month, via diplomatic channels", she added.
Russian Federation denied involvement in the first attack.
"The Novichok gel that was smeared on the handle of the Skripals' house was presumably transported in some device or syringe", he said.
What hasn't been determined yet is how and why these two people were poisoned.
However, other experts say the nerve agent was created to be persistent and not break down.
"It is not believed that there is a significant health risk to the public". He said 100 officers had been assigned to the case.
Hours later, an ambulance was called at around 0915 GMT to treat a woman who had lost consciousness at a house in Muggleton Road in Amesbury, where Hobson said Rowley lived.
Authorities initially believed the pair had taken a bad batch of heroin or crack cocaine. They were also treated at Salisbury District Hospital.
After spending weeks in critical condition, the Skripals slowly got better. He says both were taken to hospital on Saturday.