The home secretary has called on Russia to explain the Novichok poisoning after two people were exposed to it.
The couple, believed to be Charlie Rowley, 45, and Dawn Sturgess, 44, fell ill at a house in Amesbury, Wiltshire, on Saturday and remain critically ill.
Sajid Javid said the nerve agent was the same type as that which ex-Russian spy Sergei Skripal and his daughter Yulia were exposed to in March.
He said 100 counter-terrorism officers were working with Wiltshire Police.
“It is now time that the Russian state comes forward and explains exactly what has gone on,” Mr Javid told MPs.
He said the “strong working assumption” was that the couple came into contact with the nerve agent in a different location to the sites which had been part of the clean-up operation in near-by Salisbury after the Skripal poisoning.
“It is completely unacceptable for our people to be either deliberate or accidental targets, or for our streets, our parks, our towns, to be dumping grounds for poison,” he added.
He said he could not rule out the possibility that the Novichok found in Amesbury was from the same batch used in the Salisbury attack.
“We cannot attribute this to the same batch at this point and scientists will be looking into that,” he said.
“I’m also told that may not even be possible because of a number of factors, but we cannot rule out, of course, that it was from the same batch.”