The two suspects in the Salisbury nerve agent attack will be caught and prosecuted if they ever step out of Russia, the home secretary has warned.
Sajid Javid, however, did acknowledge "the reality is we will probably never see them in the UK".
He told the BBC the pair, thought to be from Russia's military intelligence service, the GRU, were acting on orders from the "highest level" in Moscow.
Ex-Russian spy Sergei Skripal and his daughter Yulia were poisoned in March.
The suspects are understood to have travelled to the UK from Moscow on 2 March on Russian passports, under the aliases Alexander Petrov and Ruslan Boshirov.
Two days later, police say they sprayed the nerve agent, Novichok, on the front door of Mr Skripal's home in the Wiltshire city of Salisbury, before travelling home to Russia later that day.
The attack left Mr Skripal, 66, and his 33-year-old daughter hospitalised for weeks.
Speaking on BBC One's Andrew Marr show, Mr Javid called it a "sickening and despicable" attack.
It was "unequivocally, crystal clear this was the act of the Russian state - two Russian nationals sent to Britain with the sole purpose of carrying out a reckless assassination attempt," he said.
"If they ever step out of the Russian Federation, Britain and its allies will get them and we will bring them to prosecution," Mr Javid added.
Last week, the UK secured the support of the US, France, Germany and Canada at a UN Security Council meeting, at which they agreed with the UK's assessment that Russia's government "almost certainly" approved the poisoning.
Russia dismissed the UK's evidence as "lies" and accused it of "disgusting anti-Russian hysteria".
Prosecutors cannot apply to Russia for the men to be extradited because Russia does not have extradition agreements with the UK.
However, a European Arrest Warrant has been obtained, should they travel to the EU.
The Crown Prosecution Service (CPS) believes there is enough evidence to provide a "realistic prospect of conviction".
Mr Javid said the GRU operated on a "very short leash from the Kremlin".
He described it as a "very well-disciplined organisation" which would "only act with orders from the highest level of the Russian government".
Mr Javid stopped short of naming President Vladimir Putin as being behind the orders but said "we all know what's at the top of the Russian government".
He went on to say that the UK had "considerable powers" to respond to Russia.
"We will bring all those powers, both overt and covert, to bear on Russia and what it represents today."