Home Secretary Amber Rudd has visited the hospital where three people who came into contact with a nerve agent in Salisbury are being treated.

Ms Rudd was filmed heading into Salisbury District Hospital, where Sergei Skripal, a former Russian spy, and his daughter Yulia, remain in a "very serious" condition.

During her visit Ms Rudd is known to have met the third victim of the attack, Nick Bailey, a police sergeant who was among the first on the scene after Mr Skripal and his daughter were found collapsed in Salisbury town centre.

He is in intensive care but is reportedly conscious and able to speak.

As many as 21 people, among them a number of police officers, have been treated in connection to the nerve agent attack, according to Wiltshire police.

It was not immediately clear whether Ms Rudd had been able to meet Mr Skripal or his daughter.

Ahead of her hospital visit, the home secretary visited the area where Mr Skripal and his daughter were found following the attack.

She also met first responders at Salisbury Guildhall and praised the emergency services, saying she was "in awe" of the their efforts.

Police are continuing to investigate the attack on Mr Skripal and his daughter, which is being treated as attempted murder.

Specialist military units were moved up to Salisbury on Friday to help with the investigation.

A police statement said the military were called in "to remove a number of vehicles and objects from the scene in Salisbury town centre".

It is understood that more than 100 personnel from the Royal Marines, the RAF and chemical teams are helping to remove the vehicles from the scene.

Scotland Yard said the military presence was due to their specialist expertise and was not a cause for concern.

"The public should not be alarmed [that military units have been deployed] and the public health advice remains the same," a police statement said.

The case is being likened to the murder of ex-Russian spy Alexander Litvinenko, who died in the UK 12 years ago after being poisoned with the radioactive element polonium 210.

A public inquiry concluded in 2016 that Mr Litvinenko's killing had "probably" been carried out with the approval of Russian President Vladimir Putin.

On Thursday, Prime Minister Theresa May told ITV News that, should evidence prove the attack on Mr Skripal was state-sponsored, Britain would do "what is appropriate".