While authorities aren't ready to link this incident to the one from earlier this year, British home secretary Sajid Javid said, "That is clearly the main line of inquiry".
"It is now time that the Russian state comes forward and explains exactly what has gone on", he said, noting the global focus on Russia as it hosts the football World Cup.
"It is completely unacceptable for our people to be either deliberate or accidental targets, or for our streets, our parks and towns to be dumping grounds for poison", he told parliament.
Police say Sturgess and Rowley were poisoned by the same lethal toxin developed by the Soviet Union that nearly killed Skripal and his daughter in March. But they continued investigating and now believe the couple has been exposed to the military-grade chemical weapon known as Novichok.
The Metropolitan Police force said this morning that "following further tests of samples from the patients, we now know that they were exposed to the nerve agent after handling a contaminated item". They did not elaborate.
Forensic investigators in hazardous material suits and gas masks have started searching both John Baker House in Salisbury and the property on the King's Gate estate in Salisbury.
Police say specialists have determined that a British couple in their 40s who visited the city of Salisbury were poisoned by the same lethal toxin - developed by the Soviet Union - that nearly killed Sergei and Yulia Skripal in the same English city in March. Sturgess and Rowley have no known links to Russian Federation.
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The police are working hard and doing their best, it's the least we can do.
The Kremlin's spokesman says Russian Federation is concerned but has had nothing to do with either poisoning case.
"We are keeping an open mind as to the circumstances regarding this incident and will continue to work closely with partners to progress our enquiries", Mills told reporters. Later that afternoon, an ambulance returned for Mr Rowley, after he started rocking against a wall, sweating, drooling, and making odd noises, according to an account by his friend.
Counter-terrorism police took over the investigation on Wednesday after the exposure to Novichok was confirmed.
Speaking to BBC security correspondent Frank Gardner, the source said Novichok could be degraded by rainwater and sunlight over time - meaning it was probably discovered by the couple in a contained space. They may return, police said.
The incident in Salisbury sparked a diplomatic dispute between the United Kingdom and Russian Federation after British investigators blamed Moscow for the attack.
Moscow has hit back by expelling Western diplomats, questioning how Britain knows that Russian Federation was responsible and offering its rival interpretations, including that it amounted to a plot by British secret services.