UK authorities say a cat and two guinea pigs owned by Sergei Skripal are dead following his poisoning

A cat and two guinea pigs owned by the former double agent poisoned in the UK are dead, the British government confirmed late Thursday after questions were raised by Russia.

Nearly a month after Sergei Skripal and his daughter Yulia were attacked with a nerve agent in the English city of Salisbury, prompting a global diplomatic crisis, the fate of the ex-spy's pets was made public.

"When a vet was able to access the property, two guinea pigs had sadly died," a spokeswoman for Britain's Department for Environment, Food and Rural Affairs told AFP.

"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. This decision was taken in the best interests of the animal and its welfare," she added.

British counter-terror police have said the Skripals first came into contact with a nerve agent at the house, with the highest concentration found on the front door.

Global attention since the March 4 attack has focused on the political fallout -- after Britain blamed Russia for the attack -- and the condition of the human victims.

It was not until this week that Moscow raised concerns over the welfare of the pets.

"Where are the animals, what state are they in? Why has the British side... not mentioned this fact? We are talking about living organisms, and if toxic agents were used then living organisms must have suffered," foreign ministry spokeswoman Maria Zakharova said on Wednesday.

The Sun tabloid said Skripal's cat was named Nash Van Drake and was taken to the nearby British defence laboratory at Porton Down where the pet was put down.

The remains of the cat and the guinea pigs were incinerated, the newspaper said citing unnamed government sources.

Russia's embassy to London earlier referred to a second missing cat, which was not mentioned by the British government.

Moscow has vehemently denied being involved in the nerve agent attack and has reacted to the expulsion of Russian diplomats from Britain and its allies with equal measures.