A huge police inquiry was launched after former Russian double agent Sergei Skripal, 66, and his daughter Yulia, 33, were found slumped on a bench in Salisbury, Wiltshire, on March 4.
And on Monday, British Prime Minister Theresa May told parliament the nerve agent used to poison the pair was a military-grade type developed by Russia.
Foreign Minister Sergei Lavrov denied the claims and said officials had demanded access to the agent following the inflammatory allegations against the former Soviet union.
He added Russia also asked to be informed about the investigation, but its requests had been “denied”.
”Russia is not guilty. Russia is ready to cooperate according to the Chemical Weapons Convention if Britain takes the trouble and condescends to carry out its international obligations according to the same document,” Mr Lavrov added.
The incident has led to a major diplomatic incident between the two countries – sparking fears the dramatic incident could lead to World War 3.
Is Russia in NATO?
Russia is currently not a member of NATO and it is thought to be unlikely the former Soviet state will ever join the political union.
However, the idea Russia could join up at some point has frequently been floated.
During a series of interviews with filmmaker Oliver Stone, President Vladimir Putin himself claimed he mooted the possibility of Russia joining NATO to Bill Clinton when he visited Moscow in 2000.
Mr Putin said: “During the meeting I said, ‘Let’s consider an option that Russia might join NATO. Mr. Clinton said ‘Why not?’ but the US delegation got very nervous.”
Russia has long held a terse relationship with NATO and NATO-member states.
Russian war games held last September were described as “a large-scale military attack against Nato“ by the commander of the Estonian Defence Forces.
Riho Terras claimed Russia’s Zapad (or “West”) exercises were used to simulate a conflict with the US-led alliance and show off Russia’s ability to amass large numbers of troops at extremely short notice in the event of a conflict.
The drills – which were held in Belarus, the Baltic Sea, western Russia and its Kaliningrad outpost between 14 and 20 September last year – depicted a fictional scenario concerned with attacks by militants.
How close to the UK is Russia?
As the crow flies, the distance between London and Moscow is 2,503 kilometres of 1,555 miles.
The distance by land transport between the two capitals is 1796 miles and takes a route through the Benelux countries, Germany, Poland and Belarus before finally reaching Russia.
In nautical miles, the distance is 1345.9.
In terms of time different, Russia is three hours ahead of the UK and measures time in MSK (Moscow Standard Time).