Two people got sick while eating at a restaurant in Salisbury, the English city where former Russian agent Sergei Skripal and his daughter Yulia were poisoned in March, police said.
Police were called to the Prezzo restaurant in the evening in response to a "medical incident" involving a man and a woman, Wiltshire police said in a statement Sunday.
"As a precautionary measure, the restaurant and the surrounding roads have been cordoned off while the agents attend the scene and establish the circumstances that led them to get sick," he said.
Britain has said that Russian officers used the nerve agent Novichok to attack the Skripals. The Kremlin has denied any participation.
Police said they had left a nerve toxin in the front door of the Skripals' house. They were found collapsed in downtown Salisbury after visiting Bishop's Mill and Zizzi Pub, another Italian restaurant.
The former Russian spy and his daughter survived the assassination attempt, but a disconnected woman, Dawn Sturgess, died in July and her partner Charlie Rowley fell ill after Rowley found a perfume bottle containing the same nerve agent.