PM says global expulsions are a warning to Moscow to respect international law
Theresa May has hailed the "unprecedented series of expulsions" of Russian diplomats across the globe in the wake of the nerve agent attack in Salisbury.
The Prime Minister insisted the move sent a strong message to Moscow that it cannot ignore international law.
The comments came as Ireland became the 24th country to join the the UK in diplomatic action against the Kremlin.
With Downing Street saying that more than 115 Russian diplomats had been ordered home by friends and allies, Dublin added one more to the list.
Mrs May's spokesman said the PM told the Cabinet the move against Russia was "an unprecedented series of expulsions that has demonstrated to the Kremlin that we will not tolerate their attempts to flout international law, undermine our values or threaten our security".
The Prime Minister added: "It is also important to note that our partners are not only taking these measures out of solidarity with the UK, but also because they recognise the threat that these Russian networks pose to the security of their own countries and the pattern of Russian aggression which has affected us all."
Irish deputy premier and foreign minister Simon Coveney said: "The use of chemical weapons, including the use of any toxic chemicals as weapons, by anyone, anywhere, is particularly shocking and abhorrent.
"The attack in Salisbury was not just an attack against the United Kingdom, but an affront to the international rules-based system on which we all depend for our security and well-being."
Ahead of the anticipated expulsion announcement, Russia's ambassador to Ireland, Yury Filatov, warned against any action that might "ruin" the relationship between the two countries.
On Monday night, Australia moved to back the UK by expelling two Russian diplomats.
Prime Minister Malcolm Turnbull and minister for foreign affairs Julie Bishop issued a statement saying two Russian diplomats identified as "undeclared intelligence officers" would be directed to leave the country within seven days.
The statement added: "This decision reflects the shocking nature of the attack - the first offensive use of chemical weapons in Europe since the Second World War, involving a highly lethal substance in a populated area, endangering countless other members of the community."
Sergei Skripal and his daughter Yulia were left critically ill following the Salisbury attack, with the PM saying doctors have indicated their condition is unlikely to change in the near future and they "may never recover fully".
In Moscow, President Vladimir Putin's spokesman, Dmitry Peskov, hinted the Kremlin would respond with tit-for-tat expulsions, saying Russia would proceed from the "principle of reciprocity".
Russia has already ordered 23 British diplomats to leave in response to the expulsion of a similar number of undeclared Russian intelligence officers from the UK.
The Russian foreign ministry said: "This provocative gesture of notorious solidarity with London, made by countries that preferred to follow in London's footsteps without bothering to look into other circumstances of the incident, merely continues the policy of escalating the confrontation."
Meanwhile, Foreign Secretary Boris Johnson has resisted calls for the England football team to boycott the World Cup in Russia in the wake of the Salisbury incident.