U.K. identifies over 200 witnesses after nerve agent attack of ex-Russian spy and daughter

British police have identified over 200 witnesses and are looking at more than 240 pieces of evidence in their investigation into a nerve agent attack on a Russian ex-spy and his daughter, the interior minister says.

Investigators summoned as Sergei Skripal and daughter remain in critical condition in Salisbury

British Home Secretary Amber Rudd, right, is seen on Friday as Kier Prichard, Chief Const. of Wiltshire police, shows her the location where Sergei Skripal and his daughter Yulia were found after having been poisoned by a nerve agent in Salisbury. (Jack Taylor/Getty Images)

British police have identified over 200 witnesses and are looking at more than 240 pieces of evidence in their investigation into a nerve agent attack on a Russian ex-spy and his daughter, the interior minister says.

After chairing a meeting of the U.K. government's emergency response committee, Amber Rudd said more than 250 counter-terrorism police were involved in the investigation, which was proceeding with "speed and professionalism."

It's the second such meeting for the COBRA (Cabinet Office Briefing Room A) committee in less than a week, as Sergei Skripal, 66, and his daughter Yulia, 33, remain in critical condition in hospital.

British officials say Skripal and his daughter were exposed to a rare nerve agent of undetermined origin.Their prognosis is unclear and officials have not said if they have suffered irreversible damage.

Skripal and his daughter Yulia, seen in a composite photo, were found slumped on a park bench last Sunday outside a shopping centre in the southern English town of Salisbury. (Misha Japaridze/AP; Yulia Skripal/Facebook via AP)

Rudd led Saturday's talks and briefed senior cabinet ministers, including Foreign Secretary Boris Johnson, on the police investigation.

Nearly a week has passed since father and daughter were found unconscious on a public bench in Salisbury in southern England last Sunday.

A police officer who was one of the first to attend the scene and was subsequently hospitalized is said to be making good progress and is now able to talk, although he remains in serious condition. Det.-Sgt. Nick Bailey had visited Sergei Skripal's home after the discovery of the pair in the centre of the cathedral town.

Wiltshire Police, the local force, issued a statement on Bailey's behalf in which he thanked the public for messages of support he has received.

Forensic police work at a cemetery in Salisbury on Saturday where ex-spy Sergei Skripal's wife is buried and where a memorial to his son stands. (Neil Hall/EPA-EFE)

"He does not consider himself a 'hero.' He states he was merely doing his job," the statement said.

Large military presence

About 180 members of the armed forces, including chemical warfare experts, are now on the ground in Salisbury helping Scotland Yard's anti-terrorism unit in the investigation. 

On Friday, their attention switched focus to a cemetery in Salisbury where Skripal's wife is buried and a memorial for his son is located. Skripal's wife, Lyudmila, 59, died of cancer in 2012. His son Alexander, 43, died while on holiday in St. Petersburg last year after reportedly suffering from liver failure.

British authorities have not yet revealed what substance was used to threaten the lives of the former Russian spy and his daughter. (CBC)

Special tents have been set up over the two sites as experts in hazmat suits scour the area for clues.

Earlier Friday, members of the armed forces removed a police car used in the initial response from Salisbury district hospital.

Other vehicles, including ambulances, were expected to be taken away for inspection on Saturday.

Meanwhile, experts are also continuing to examine the nerve agent used in the attack in the hope it will lead to whoever was responsible.

Members of the Falcon Squadron, Royal Tank Regiment, conduct final training on Friday in southern England before deploying to Salisbury to help investigate the nerve-agent poisoning of a former Russian spy. (Cpl. Pete Brown/U.K. Ministry of Defence via AP)

Skripal betrayed dozens of Russian agents to British intelligence before his arrest in Moscow in 2004. He was sentenced to 13 years in prison in 2006, and in 2010 was given refuge in Britain after being exchanged for Russian spies.

The incident has been likened to the case of former KGB agent Alexander Litvinenko, a critic of Russian President Vladimir Putin, who died in London in 2006 after drinking green tea laced with radioactive polonium-210.

Britain has said it will respond robustly if evidence shows Russia was behind the attempted murder. The Kremlin has denied any involvement in the incident and says anti-Russian hysteria is being whipped up by the British media.

With files from Reuters