Moscow is awaiting almost two dozen Russian diplomats ordered to leave Britain as part of a standoff over a nerve agent attack on British soil.
The latest tit-for-tat exchange between London and Moscow comes after a show of solidarity with Britain by the European Union and North Atlantic Treaty Organisation on March 19, both of which strongly condemned the March 4 attack on Sergei Skripal and his daughter, Yulia, with a deadly nerve-agent developed by the Russian military.
Investigators from the global Organisation for the Prohibition of Chemical Weapons (OPCW) arrived in Britain on Monday to collect samples of the nerve agent.
The father and daughter remain in a critical condition in hospital following their exposure to the lethal nerve agent, Novichok.
Moscow announced the measures on the eve of a presidential election which incumbent Vladimir Putin should comfortably win. "The first thing that entered my head was that if it had been a military-grade nerve agent, the people would have died on the spot", he said.
"It is going to take weeks, possibly months", Mr Basu told BBC Radio 4's Today programme, adding: "This is going to be frustrating for people".
Foreign Secretary Boris Johnson said the trail of blame for the poisoning of former Russian spy Sergei Skripal and his daughter Yulia in the English city of Salisbury "leads inexorably to the Kremlin".
"We agreed to say that the European Union needs to provide a firm response, and not just a symbolic one", Polish Prime Minister Mateusz Morawiecki said.
Trump says will meet with Putin 'in the not too distant future'
He has also spoken about the need to avoid another arms race, despite using his pre-election address to showcase new Russian arms. He said that during their hoped-for meeting the two men would likely discuss Ukraine, Syria and North Korea, among other things.
Top EU diplomats were expected to discuss next steps at a meeting Monday, with some calling for a boycott of the upcoming World Cup in Russian Federation.
Responding to Russia's decision to expel the diplomats, Britain said it had "anticipated" the move.
The UK Government believes the Russian state ordered the attack - a claim it strenuously denies.
Britain says the Skripals were poisoned with a Russian-made nerve agent, in violation of an global ban on chemical weapons.
"Immediately, a new spiral of anti-Russia campaign has surfaced embodied in statements of the United Kingdom prime minister", she said.
Leonid Rink says the agent dubbed Novichok in the West had a different name when it was designed as a chemical weapon in the Soviet Union.
The Prime Minister chaired a National Security Council meeting, with her spokesman saying other measures were still being considered and could be deployed at "any time". She said the Russian Foreign Ministry is summoning ambassadors Wednesday to present Moscow's arguments and raise questions about the case.
British police appealed Saturday for witnesses who can help investigators reconstruct the Skripals' movements in the crucial hours before they were found unconscious.
On March 18, in his first public remarks on the poisoning, Putin flatly rejected Britain's accusations, telling reporters as he was headed for a landslide reelection, that Russian Federation "has no such" weapon.