- Video report by ITV News Security Editor Rohit Kachroo
A police officer who fell seriously ill after attending to the victims of a nerve agent attack in Salisbury is "engaging, awake and talking" in hospital, although he remains seriously unwell, the Home Secretary has said.
Former Russian spy Sergei Skripal and his daughter Yulia, who were found slumped on a bench on Sunday, remain critically ill.
Amber Rudd called the attack a "brazen and reckless act" as she gave an update on the conditions of the victims of what the police called an attempted murder using a nerve agent.
"The two targets are in intensive care, they are very seriously ill," she said, adding: "The policeman is still seriously unwell but he is actually engaging, awake and talking to people."
She earlier told Good Morning Britain she was "optimistic" for the police officer but said "it's too early to say".
Hundreds of police officers are continuing to investigate who was behind the attempted murder of the double agent and his daughter.
Counter-terror police have urged any members of the public who visited Salisbury town centre on Sunday to come forward.
The case has already drawn parallels with the death of ex-Russian spy, Alexander Litvinenko, who died in the UK 12 years ago after being exposed to polonium.
The incident prompted crisis talks in Whitehall, and has led to a souring of already strained relations between Russia and the UK.
Amber Rudd told the Commons the attack was "attempted murder in the most cruel and public way" adding: "We must avoid speculation and allow police to continue their investigation."
The defence secretary Gavin Williamson called Russia "an ever-greater threat," but he declined to say whether he held Russia responsible for the attack in Salisbury.
He told Good Morning Britain: "What's happened is absolutely disgusting and it is so important we give the police the space and opportunity to do a proper and thorough investigation."
An emergency Cobra meeting was convened on Wednesday, while Foreign Secretary Boris Johnson has described Russia as a "malign and disruptive force".
A Kremlin spokesman described Mr Skripal's illness a "tragic situation", but added that it didn't have "any information".
The Russian Foreign Ministry accused Western media of using the incident to "incite an anti-Russian campaign".
Skripal, 66, is a former Russian spy who is believed to have worked for MI6. He was arrested in Moscow in 2004.
In 2010 he was granted refuge in the UK following one of the biggest spy swaps since the Cold War.
Teams in protective suits and masks are continuing to search the Bishop's Mill Pub and Zizzi in the city centre which the pair visited that afternoon.
The Met Police Assistant Commissioner Mark Rowley has said incident was being treated as attempted murder "by administration of a nerve agent".
Investigators believe Mr Skripal and his 33-year-old daughter were "targeted specifically".
- What is a nerve agent?
Nerve agents work by disrupting signals in nerves, at the synapses between nerves. Different agents work in different ways and have different volatilities.
Symptoms of exposure to nerve agents may include respiratory arrest, heart failure, twitching or spasms - anything where the nerve control is degraded.
Nerve agents can cause death, but not necessarily at low-level exposure or with a minor dose.
Details around the type of nerve agent used were not disclosed, but investigators are working closely with specialists and scientists.
On Wednesday, three women who work near to the scene were taken away for hospital treatment.
But Asst Commissioner Rowley said police did not believe there was a larger health risk.
"Of course public safety remains our joint priority and this is clearly an awful incident and I know that local people will be concerned," he said.
"But I would stress that at the moment we are not seeing any evidence of a widespread health risk."
A new cordon has also been erected around the street and nearby roads where the ex-spy lived.
Evidence of foul play will put further strain on already tense relations between Whitehall and the Kremlin.
Theresa May has backed calls to boycott the World Cup in Russia if Moscow is shown to have been involved.
Mrs May told MPs at Prime Minister's Questions that the Government would "look at whether ministers and other dignitaries should attend" the tournament.