Police officers seal off a cul-de-sac in Salisbury, England, near to the home of former Russian ex-spy Sergei Skripal as a nerve agent is believed to have been used to critically injure him and his daughter Yulia. Britain's Home Secretary says the investigation into the nerve agent attack on a Russian ex-spy and his daughter is focusing on three sites — his home, a pub and a restaurant. (Andrew Matthews/PA via AP)

Police officers seal off a cul-de-sac in Salisbury, England, near to the home of former Russian ex-spy Sergei Skripal as a nerve agent is believed to have been used to critically injure him and his daughter Yulia. Britain's Home Secretary says the investigation into the nerve agent attack on a Russian ex-spy and his daughter is focusing on three sites — his home, a pub and a restaurant. (Andrew Matthews/PA via AP)

LONDON (AP) — The Latest on the poisoning of a former Russian spy in Britain and his daughter (all times local):

1:45 a.m.

British police say around 21 people have had medical treatment after a nerve-agent attack on an ex-Russian spy.

The U.K. has vowed strong action against whoever was responsible for the “brazen and reckless” act. Three people remain hospitalized after the poisoning Sunday in the southern English city of Salisbury — ex-spy Sergei Skripal, his daughter and a British police officer who tried to help them.

ADVERTISEMENT

___

8:45 p.m.

A Russia expert in Britain says that “Russia was the most likely story” for explaining who was behind a nerve agent attack on a former Russian spy and his daughter.

But Sam Greene, director of the Russia Institute at King’s College London, cautioned against assuming it was the result of direct orders from the Kremlin.

Greene told Sky News that “Russia does seem like the most likely story” given “the fact that we have seen things like this before.”

Greene also said that even if the attack was planned in Russia, it may not have been ordered by the Kremlin.

Greene said that “a lot of these things are being done by people operating at sort of an arm’s length’s distance from the command and control structure.”

___

6:55 p.m.

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.

___

5 p.m.

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.

ADVERTISEMENT

___

11:45 a.m.

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 it’s 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.

___

9:10 a.m.

Britain’s Home Secretary says the investigation into the nerve agent attack on a Russian ex-spy and his daughter is focusing on three sites — 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.”