LONDON ó British police now say a total of roughly 21 people have sought treatment after a nerve agent was used to attack and ex-Russian spy and his daughter.Wiltshire acting police chief Kier Pritchard told Sky News on Thursday that "a number" of those people got blood tests, support and hospital advice.He says only three people remain hospitalized. They are former Sergei Skripal, his daughter Yulia and police Sgt. Nick Bailey.Officials say Bailey is making progress. The ex-spy and his daughter remain in critical condition.Police say the roughly 21 people treated include the three still hospitalized.Read More: Why did Putin target Tampa Bay?The global chemical weapons watchdog says it is in touch with authorities in Britain about the use of a rare nerve agent in an attack on a former Russian spy and his daughter.In a brief written statement, the Organization for the Prohibition of Chemical Weapons says that "the recent report that two people became seriously ill in the United Kingdom as a result of exposure to a nerve agent is a source of great concern."The organization based in The Hague did not immediately return a call Thursday seeking more detail on the nature of the contacts with Britain.British Home Secretary Amber Rudd has told the House of Commons that enormous resources are being used to determine who is responsible for poisoning Sergei Skripal, 66, and his daughter, Yulia, 33. The pair were found unconscious on a bench in the city of Salisbury on Sunday.British Home Secretary Amber Rudd says a former Russian spy and his daughter who were poisoned with a nerve agent are in a critical but stable condition.Sergei Skripal and his daughter Yulia were found unconscious in the English city of Salisbury on Sunday.Rudd says a police officer who treated them is in serious but stable condition and is "talking and engaging." She says itís highly likely the officer was exposed to the same nerve agent.Rudd says the attack is an "outrageous crime" and a "brazen and reckless act" but cautions it is too early to say who was behind it.Britainís Home Secretary says the investigation into the nerve agent attack on a Russian ex-spy and his daughter is focusing on three sites ó his home, a pub and a restaurant.Amber Rudd told the BBC on Thursday that enormous resources are being directed at trying to figure out who might be responsible for the poisoning of Sergei Skripal and his daughter, Yulia.Rudd, who is in charge of public security issues, says the police officer also injured in the incident Sunday is also in serious condition but is conscious and talking.Rudd declined to say if she believed Russia was behind the attack, but says Britain will "if it is appropriate, attribute it to somebody. If that is the case, then we will have a plan in place."