The British military has been deployed to help police investigating the poisoning of a former Russian spy and his daughter, as attention moved to the burial site of his wife and son.

Around 180 troops were deployed in Salisbury following the nerve agent attack on Sergei Skripal and his daughter Yulia.

Scotland Yard requested specialist help to remove vehicles and objects from scenes across the city amid fears of contamination.

Home Secretary Amber Rudd will chair the British government's emergency Cobra meeting on Saturday to be updated on the investigation.

Officers in hazmat suits were sent to Salisbury's London Road cemetery, where a tent was erected over the memorial to Mr Skripal's son Alexander, who was cremated last year.

Officers also sealed off the gravestone of Mr Skripal's wife Liudmila, who was buried there in 2012.

Police say their deaths are part of the investigation into the poisoning of Mr Skripal and his daughter Yulia, who were found slumped on a park bench in Salisbury on Sunday evening.

They remain in a serious condition in hospital, along with Detective Sergeant Nick Bailey who was also exposed to the nerve agent.

Mrs Rudd, who visited the city centre and hospital where Mr Bailey is being treated, warned the government was "committed to doing all we can to bring the perpetrators to justice - whoever they are and wherever they may be".

Russia's foreign minister said the country would consider helping UK authorities investigate the poisoning after the Kremlin denied involvement.

Sergei Lavrov seemed to resent suggestions that Moscow was behind the nerve agent attack on the Skripals, calling such claims "propaganda".

Skripal served four years of a 13 year sentence in Russia after he was caught spying for MI6 and was released as part of a spy exchange in 2010, when he was given refuge in the UK.