The Russian foreign ministry has ordered Britain to reduce the number of diplomats in Moscow down to the same amount that Russia has in London as the row over the Salisbury attack.
Ambassadors from more than 20 countries were called into the foreign ministry in Moscow to be told of the latest wave of retaliatory measures being imposed by the Kremlin.
The UK expelled 23 Russian diplomats in the wake of the poisoning of Sergei Skripal, 66, and his daughter Yulia with the nerve agent Novichok.
Laurie Bristow, the UK ambassador in Moscow, was among those called into the ministry.
He told reporters: "It is important to bear in mind why this crisis has arisen in the first place.
"It's the use of a chemical weapon on the streets of the United Kingdom that has threatened the lives of a number of people in my country.
"We asked certain questions of the Russian state and have still not received adequate answers."
Russia has told a number of countries - including Ireland, Germany, Italy, France, Spain, Finland, Poland, the Czech Republic, the Netherlands and Norway - they must send home the same number of diplomats as they had ordered to leave their nations.
A spokesman for Ireland's deputy premier, Tanaiste Simon Coveney, said: "There is no justification for this expulsion.
"Our staff do not engage in activities which are incompatible with their diplomatic status. This decision to expel an Irish diplomat is regrettable."
So far, more than 150 Russian diplomats, some of whom are suspected spies, have been told to return home by the UK's allies.
The Russian Embassy said on Friday it "insists" on the right to see Ms Skripal, 33, after it emerged on Thursday she was improving rapidly.
She spent three weeks in a critical condition after being exposed to Novichok on March 4.
The Russian Embassy said in a tweet: "Good news as Yulia Skripal is reported as recovering well. We insist on the right to see her, in accordance with the 1968 Consular Convention."
Ms Skripal's father remains in a critical but stable condition in hospital.
Late on Friday afternoon, the Russian Embassy published a list of 27 questions it claimed it had for the British authorities over the treatment of the Skripals.
The list included demands to know the exact nature of their condition and how they were being treated, and whether British doctors' approach "helped or harmed" the Skripals.
It also claimed Mr Skripal's niece had been inquiring after her uncle's health but that she had been ignored by the Foreign Office, and wondered why no images or footage of the Skripals alive in hospital had been published.
Russian foreign minister Sergei Lavrov said Moscow would retaliate by expelling the same number of diplomats that each country had ejected.
The ministry said it summoned the British ambassador on Friday following the "provocative and unsubstantiated actions by Britain, which instigated the expulsion of Russian diplomats from various nations for no reason".
The British Government was given 30 days to reduce its diplomatic personnel to the same number of diplomats that Russia has stationed in the UK.
The number of British diplomats that will have to leave Russia was not immediately clear.
A spokeswoman for the Foreign and Commonwealth Office said: "It's regrettable but in light of Russia's previous behaviour, we anticipated a response.
"However, this doesn't change the facts of the matter. The attempted assassination of two people on British soil, for which there is no alternative conclusion other than that the Russian state was culpable.
"Russia is in flagrant breach of international law and the Chemical Weapons Convention and actions by countries around the world have demonstrated the depth of international concern."
She said the FCO would not be commenting on the details of the meeting.
Scotland Yard believes Mr Skripal and his daughter, who was visiting him from Russia, first came into contact with the deadly chemical at his home.
Detailed forensic testing revealed the highest concentration of Novichok was found on the front door.
The vast attempted murder investigation continues to unfold in the Wiltshire city, most recently leading police to cordon off a children's play area at Montgomery Gardens.
Detectives said traces of the nerve agent had been found at some of the other scenes where investigations had been carried out, but at lower concentrations.
Efforts will now focus in and around the address, and specialist teams will step back from some of the other areas investigated over the past few weeks.
Mr Skripal and his daughter have been patients at Salisbury District Hospital since they were discovered unconscious on a park bench close to The Maltings shopping centre nearly four weeks ago.
Wiltshire Police Detective Sergeant Nick Bailey, who was also exposed to the nerve agent, was discharged from the hospital last week.