A relative of a former Russian spy and his daughter who were poisoned in Britain said Friday that she has not heard from them since a call from the daughter on Thursday, but she is certain that call was authentic. Sergei Skripal and his daughter Yulia are in a British hospital after being poisoned with a military grade nerve agent called novichok.

Britain has blamed Russia for the attack, saying Vladimir Putin's government bears responsibility either for orchestrating it, or for losing control of the illegal chemical weapon it produced and allowing it to be used in an assassination attempt on English soil.

Russian state television on Thursday played back a recording of what they said was a phone call from Yulia Skripal to her cousin Viktoria, who lives in Russia. There was no explanation of how the call was recorded, and Viktoria is heard on the call expressing surprise at hearing her cousin, who was in critical condition until a week ago.

Sergei Skripal's condition also has improved. Salisbury District Hospital director Dr Christine Blanshard said in a statement on Friday that he was, "responding well to treatment, improving rapidly and is no longer in a critical condition."

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Viktoria Skripal told The Associated Press and BBC News on Friday that she had no doubt that it was Yulia who called, and that she had not heard from her since. Viktoria, who works as a chief accountant in the city of Yaroslavl, explained to the AP that the call was recorded because she has an app on her phone that she uses to keep track of all the calls she makes for work.

She said she was invited to come to the British Embassy on Friday afternoon, supposedly to pick up her visa, but a contact at the embassy emailed her to say that the appointment had been canceled and that the decision on her visa application had not been made yet.

Meanwhile, a Russian Foreign Ministry spokeswoman questioned Friday why British officials incinerated the pets found at the poisoned ex-spy's home.

It turns out Sergey Skripal has two cats and two guinea pigs. Were they also poisoned? Where are they and how are they treated? Important questions for the investigation. Read our comment: https://t.co/T8vwYdz77A pic.twitter.com/J5w3Jpz2I0 — Russian Embassy, UK (@RussianEmbassy) April 5, 2018

Maria Zakharova said on Facebook that the two guinea pigs and a cat who lived in Sergei Skripal's home were important evidence.

Britain's Department for Environment, Food and Rural Affairs said the guinea pigs were found dead at Skripal's home after it was sealed off for investigations. It said the cat was also found "in a distressed state and a decision was taken by a veterinary surgeon to euthanize the animal to alleviate its suffering."

Britain has blamed Russia for the March 4 novichok nerve agent attack on Skripal and his daughter. In response, more than two dozen Western allies including Britain, the U.S. and NATO have ordered out over 150 Russian diplomats in a show of solidarity.

Moscow has fiercely denied its involvement in the nerve agent attack and expelled an equal number of envoys. The diplomatic turmoil has hit lows unseen even at the height of the Cold War.

Russia accuses Britain of waging a deliberate defamation campaign.

At a meeting Thursday of the United Nations Security Council, Russia's ambassador pushed back hard against allegations, saying British officials were "playing with fire" and would be sorry.

It was one of the most contentious Security Council meetings in recent years, reports CBS News' Pamela Falk, with blistering threats by Russia and accusations by Britain -- but all without any conclusion. The meeting took place about a week before the independent analysis of the nerve agent samples is expected to be completed by the global chemical weapons watchdog, the Organization for the Prohibition of Chemical Weapons (OPCW).

Russian ambassador Vassily Nebenzia claimed Russia was the victim of a hasty, sloppy and ill-intentioned defamation campaign by London and its allies.

Moscow assumes "with a high degree of probability" that the intelligence services of other countries are likely responsible for the incident, Nebenzia said at the U.N.

As CBS News' Charlie D'Agata reported Friday on "CBS This Morning," the Kremlin's version of the story -- pushed hard by state-controlled media since the moment Russia was accused of the nerve agent attack -- is being widely accepted by residents in Moscow.