ALSO READRussia ex-spy poisoning 'extremely worrying': Chemical weapons watchdog UK national security chiefs to meet as pressure over spy probe mounts UK media: Traces of nerve agent found in ex-spy poisoning Russian spy poisoning: Police seeking nerve agent source UK to hold emergency meeting on Russian spy attack
It said the UK's threat of "punitive" measures would "meet with a response".
Downing Street says the Prime Minister has received the backing of US President Donald Trump, who agreed in a phone call that Moscow "must provide unambiguous answers as to how this nerve agent came to be used".
A spokesman also said France's President Emmanuel Macron and German Chancellor Angela Merkel, as well as Estonia, Latvia and Lithuania - Baltic states bordering Russia - have all condemned the attack and offered support to the UK.
Foreign Secretary Boris Johnson said if the attack was shown to be a "direct act" by the Russian state it would be a "clear violation of the chemical weapons convention, a breach of international law and a threat to those who abide by the rules-based international order".
It also contended international obligations required a joint investigation take place into the incident.
Another tweet said it had sought an "explanation" from the Foreign Office, amid speculation the UK could mount a cyber-attack, as it "takes a serious view on cyber security breaches".
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)