"It was initially believed that the two patients fell ill after using possibly heroin or crack cocaine ... However, further testing is now ongoing."
LONDON — British police declared a "major incident" early Wednesday after two people were left critically ill following their suspected exposure to an "unknown substance" just a few miles from the scene of a nerve agent attack on a former Russian spy and his daughter.
Emergency officials found a man and a woman — both aged in their 40s — unconscious at a property in Amesbury, England, on Saturday.
"It was initially believed that the two patients fell ill after using possibly heroin or crack cocaine from a contaminated batch of drugs," Wiltshire Police said in a statement. "However, further testing is now ongoing to establish the substance which led to these patients becoming ill and we are keeping an open mind as to the circumstances surrounding this incident."
The force added that the pair "might have been exposed to an unknown substance."
Amesbury is seven miles from the town of Salisbury, where former double agent Sergei Skripal and his daughter were poisoned with military-grade nerve agent Novichokin March. The British government pinned the attack on the Russian state.
Police emphasized that it was unclear whether a crime had been committed in the latest case.
However, several locations frequented by the couple around Amesbury and Salisbury were cordoned off as a "precautionary measure." They included a Baptist church.
Amesbury is located around five miles from Stonehenge, the prehistoric monument visited by more than a million people annually.
Salisbury District Hospital, where the pair are receiving treatment and the Skripals were patients in the aftermath of the March attack, remained open as normal on Wednesday.