British Prime Minister Theresa May will chair a meeting of her national security team on Monday after weekend confirmation that traces of a nerve agent used in the attempted murder of a Russian former double agent were found in a pub and a restaurant he visited.
May and senior ministers will receive an update on the investigation into the attack on the spy.
The 4 March attack on 66-year-old Sergei Skripal and his daughter has mounted pressure in Britain for answers over the incident.
May is reportedly on the brink of publicly declaring Russia's involvement, possibly following the national security council meeting.
She is considering a raft of "hard line" responses, with diplomatic expulsions and rescinding the visas of Kremlin-linked residents among the possible measures, it added.
The Russian pair was found slumped on a bench in Salisbury, southwest England, and remain in a critical but stable condition in hospital.
Authorities have yet to confirm the precise substance involved in the attack.
Sally Davies, England's chief medical officer, revealed that people who may have come into minimal contact with the nerve agent should wash their clothes and belongings as a precaution.
Meanwhile, Britain's armed forces are expected to continue assisting police in the probe today.
Around 180 troops, including chemical warfare experts, have been deployed in Salisbury after investigators requested expert assistance.
Interior Minister Amber Rudd has said police were examining more than 200 pieces of evidence, had identified more than 240 witnesses, and were plowing through security camera footage.
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