Vladimir Putin dismissed claims of Russian involvement in the Salisbury spy poisoning as "nonsense" as he was re-elected president of the Federation.
Sergei Skripal and his daughter Yulia would have died instantly if they had been attacked with a nerve-agent, the leader claimed while he celebrated the start of another six year term.
It comes after Boris Johnson accused Russia of stockpiling the Novichok for a decade in breach of international rules.
President Putin, who secured a fourth term amid widespread claims of electoral fraud, said he learnt about the "tragedy" from the media.
"The first thing that comes to my mind is that should it really be a warfare agent, people would have died instantly. It is an obvious fact.
"Russia does not possess such agents. We have destroyed all our chemical arsenals under control of international observers."
Moscow mocked the UK, claiming the UK's response had fuelled an increase in support for President Putin in the election.
Inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) will arrive in the UK on Monday to test the nerve-agent but the results will take at least two weeks.
The Foreign Secretary said Moscow has investigated ways of delivering nerve agents for assassination over the last 10 years in a breach of international rules.
The team from The Hague will use international laboratories to carry out tests on the nerve agent.
Mr Johnson will travel to Brussels to brief foreign ministers from across the European Union at a meeting on Monday on the attempted assassinations before holding talks Nato secretary general Jens Stoltenberg.
Labour has faced intense criticism for its response to the attack after leaving open the possibility that Russia was being framed.
Shadow chancellor John McDonnell said the Salisbury incident is "highly likely" to have been a state execution, and President Putin "is responsible" for the attack whether directly or through negligence.
Russia's ambassador to the EU, Vladimir Chizhov, suggested the nerve agent may have come from the Porton Down laboratory, which is about eight miles from Salisbury.
Sweden and the Czech Republic denied Russian suggestions they may have been the source of the nerve agent.
The national security council will meet early next week to discuss Moscow's tit-for-tat response to the UK's expulsion of 23 Russian diplomats.