Sergei Skripal, 66, and his daughter Yulia remained in critical condition, while police officer Nick Bailey, who was the first to go their help on Sunday and was exposed to the nerve agent, is recovering in hospital from his serious condition.
Longer term plans would include bolstering British military capabilities in Eastern Europe and lobbying North Atlantic Treaty Organisation in July for further reinforcements, it said. The officer - I'm very sorry he's been injured - has actually been to the house, whereas there's a doctor who looked after the patients in the open who hasn't been affected at all.
Ms Rudd was seen at the bench where Mr Skripal and his daughter collapsed in the city centre, which remains cordoned off by police.
The Russian embassy in the United Kingdom, while quoting the version of British authorities negated any Russian links of the spy, in one of the tweets posted on Thursday.
The Ministry of Defense regularly assists the emergency services and local authorities in Britain.
The attack on Skripal and his daughter is reminiscent of the case of another Russian spy, Alexander Litvinenko, who was poisoned to death in London by Kremlin-linked agents in 2006.
Former Commissioner Ian Blair has backed calls from a senior Labour Party lawmaker to re-examine the deaths in light of the attack on former Russian spy Sergei Skripal and his daughter in the city of Salisbury.
Nerve agents such as sarin are highly toxic chemicals that disrupt the nervous system and shut down bodily functions.
Some 180 troops are being sent to Salisbury to help police investigating the nerve agent poisoning of former double-agent Sergei Skripal and his daughter.
Mr Skripal served four years of a 13 year sentence in Russian Federation 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.
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Russian Foreign Minister Sergey Lavrov said Moscow was "ready to consider" lending a hand, "whether it's poisoning of some British subjects, whether it's rumors about interference in the USA election campaign".
They were found unconscious on a bench, triggering a police inquiry headed by counterterrorism detectives.
"But in order to conduct such cases, it is necessary not to immediately run out on TV screens with unfounded allegations", Lavrov was quoted as saying by Russian state news agency Tass in the Ethiopian capital, Addis Ababa.
Britain's Home Secretary Amber Rudd (right) visited Salisbury on Friday..
A total of 21 people had been treated in hospital following the incident, police said.
Health chiefs have said there is a low risk to the wider public from the nerve agent used against Skripal and his daughter.
"This was attempted murder in the most cruel and public way", said Rudd, Britain's top police official.
Those branded enemies of the Russian state have sometimes died mysteriously overseas, and the Skripal case echoes the death of Alexander Litvinenko, a former Russian agent who was poisoned in London in 2006 with radioactive polonium-210.
"Of course, if action needs to be taken, then the government will do that".
The circumstances of the attack, and its echoes of the fatal poisoning of Alexander Litvinenko in 2006, have prompted questions over the Government's response if the evidence points to a state-sponsored assassination plot.