Australia has become the latest country to expel Russian diplomats in a show of support for Britain over the Salisbury nerve agent attack.
Prime Minister Malcolm Turnbull called it a "disgraceful" and "brazen" attack and said his country "cannot and will not stand by and watch when the sovereignty of our allies and partners is threatened".
Earlier, Mr Turnbull and minister for foreign affairs Julie Bishop issued a joint statement saying two Russian diplomats identified as "undeclared intelligence officers" would be directed to leave the country within seven days.
More than 100 Russian spies are being sent home from more than 20 countries, including 60 from the US and intelligence officers operating in Canada, Ukraine, Norway, Macedonia and Albania, as well as in 16 European Union member states.
Mr Turnbull said the poisoning on Sergei Skripal and his daughter, Yulia, which has left them critically ill, was "an attack on all of us".
He added: "It was an attack on the sovereignty of every nation that respect the rule of law and that is why we are taking this action today with another 23 nations around the world, we are defining this recklessness, this lawlessness, from Russia and expressing in solidarity with the United Kingdom and other nations that share those values that we will not tolerate this type of reckless undermining of international law, this reckless assault on the sovereignty of nations."
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".