Yulia Skripal with a cat, in a picture posted on her Facebook page.
CNN  — 

Two guinea pigs and a cat belonging to former Russian spy Sergei Skripal, poisoned in a nerve agent attack in the UK last month, have died, British authorities have said.

The two guinea pigs were found dead in Skripal’s house some time after the attack, apparently from dehydration, and a cat was put down after being discovered in a “distressed” state. Police sealed the house after Skripal and his daughter Yulia were discovered unconscious on a bench in Salisbury on March 4.

“When a vet was able to access the property, two guinea pigs had sadly died,” the UK Department for Environment, Food and Rural Affairs (DEFRA) said in a statement. “A cat was also found in a distressed state and a decision was taken by a veterinary surgeon to euthanise the animal to alleviate its suffering.”

The guinea pigs “most likely… died due to a lack of water,” a DEFRA spokesperosn told CNN later.

The deaths are the latest peculiar developments in a story that has taken a turn for the absurd in recent days. Apparently in an effort to shift the debate away from the issue of culpability, a succession of Russian officials have attempted to make light of the whole affair.

Investigators work in the garden of Sergei Skripal's house on March 22.

The issue of the pets was first raised by Russian Foreign Ministry spokeswoman Maria Zakharova on Wednesday. “Where are they now?” she said, speaking to reporters. “After all, we are talking about living organisms, and if a poisonous agent was used in the house, they must also have been affected,” she continued.

Later, at the United Nations Security Council on Thursday, Russia’s representative Vassily Nebenzia read out extracts from a copy of Alice in Wonderland in an attempt to discredit Britain’s claims that Russia was responsible for the Skripals’ fate.

After the death of the animals was confirmed, the Russian embassy in London said their value as pieces of evidence had been ignored. “Such treatment of pets is also hardly consistent with UK laws on animal cruelty and comes as a blatant disregard to Mr Skripal’s rights as the owner and companion of the animals,” the embassy said, claiming a second cat was still missing.

DEFRA told CNN that only one cat had been found on the property and offered no information about a possible second cat. It could not say whether there was any evidence the animals had been poisoned.

Detectives revealed last week that they believe Skripal and his daughter Yulia first came into contact with a nerve agent at the former spy’s home and that the highest concentration of the substance had been found on the front door.

Sergei Skripal remains critically ill but stable in hospital. Yulia, also poisoned in the attack, is now conscious and talking. In a statement released Thursday, the 33-year-old said she woke up “over a week ago” and her “strength is growing daily.”

Yulia and Sergei Skripal were found slumped on a bench at an outdoor shopping precinct. The British government believes they were poisoned with a Russian-made nerve agent, Novichok. Russia denies involvement and the incident has led to a spiraling diplomatic dispute between the two nations.

The UK and its allies have expelled scores of Russian diplomats, triggering retaliatory expulsions by Russia.

At the United Nations Security Council meeting on Thursday, Nebenzia, Russia’s envoy, called the allegations a “fake story” and said the UK was “playing with fire and they will be sorry.”

The British government insists that only Russia had the capability to carry out the attack.

CNN’s Katie Polglase and Sebastian Shukla contributed to this report.