British police say they believe a Russian former spy and his daughter were poisoned with a nerve agent.
Metropolitan Police counterterrorism chief Mark Rowley said the attack on Sergei Skripal and his daughter Yulia on Sunday is being treated as attempted murder.
He says police believe they were specifically targeted.
They are in critical condition in a hospital.
Rowley says a police officer who treated them when they collapsed in Salisbury on Sunday is also in serious condition.
Chief medical officer Sally Davies said the poisoning posed a "low risk" to the general public.