British officials have said that the Skripals were sickened by a class of nerve agents known as novichoks and developed by the Soviet Union — apparently the first use of a chemical weapon on British soil since World War II. Britain has said that Russia was almost certainly to blame for the attack, and after making its case behind closed doors, London has orchestrated a coordinated international response to the poisoning with its allies on both sides of the Atlantic.
That has led to retaliatory expulsions of hundreds of government representatives, angry denunciations, and promises by Britain and its allies to inflict economic pain on Kremlin officials and their associates; the United States is expected on Friday to name dozens of wealthy Russians who will face financial sanctions.
President Vladimir V. Putin’s government has insisted that Moscow had nothing to do with the poisoning, alternately questioning whether the Skripals were really poisoned, whether a nerve agent was involved, whether it was a novichok, whether another country might have supplied it, and whether Britain itself might have carried out the attack.
The Kremlin has also seized on every apparent inconsistency in the accounts from the British government, particularly remarks by Foreign Secretary Boris Johnson, who appeared to have gone too far in saying that Mr. Putin himself was probably involved, and that the chemical came from Russia.
The Organization for the Prohibition of Chemical Weapons, an international body, is examining evidence in the case. Russia has demanded that it be allowed to take part in the investigation — a suggestion that Britain has called perverse.
Russia called a meeting of the United Nations on Thursday to proclaim its innocence, and it has even accused Britain of mistreating Mr. Skripal’s pets, which were left alone for weeks in his house after investigators sealed it off. Britain’s Department for Environment, Food and Rural Affairs said Friday that “two guinea pigs had sadly died” by the time someone entered the home to see about the animals, and that “a 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.”
On Thursday, a Russian television station broadcast a recording of what it said was a brief phone call between Ms. Skripal and a cousin in Russia.
Mr. Skripal, once a colonel in Russian military intelligence, was convicted in 2006 of selling secrets to the British and imprisoned. He was sent to Britain in 2010 as part of a spy swap. His poisoning followed the suspicious deaths of a number of Kremlin foes in Britain over more than a decade, some of which the British government is investigating anew.