British officials on Wednesday announced charges in the poisoning of an ex-Russian spy against two men they allege worked for Russia's military intelligence agency.

United Kingdom Prime Minister Theresa May said British intelligence has concluded the two men were officers for GRU, which is Russia's military intelligence operation. She added that the nerve agent attack was likely approved at a "senior level of the Russian state."

The Associated Press reported that the Crown Prosecution Service charged Alexander Petrov and Ruslan Boshirov in absentia with conspiracy to murder, attempted murder and the use of military-grade nerve agent Novichok in the attack on former Russian spy Sergei Skripal and his daughter earlier this year.

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Authorities said the two men flew from Moscow to London using Russian passports two days before the March nerve agent attack, smuggling the substance in a perfume bottle.

Police said the two men then applied the poison to Skripal's door and flew back to Russia just hours later.

The AP reports that British officials expressed skepticism that the men would be formally arrested, noting that Russian law prohibits the extradition of the country's citizens.

Russia has continually denied involvement in the attack, which left Sergei Skripal and his daughter, Yulia, gravely ill. Both survived.

The incident prompted an international response, with the United States, Britain and other European nations expelling numerous Russian diplomats.

GRU agents were also implicated earlier this year in special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE's investigation into Russian interference in the 2016 U.S. election.

Mueller indicted a dozen members of GRU for involvement in the hack of the Democratic National Committee (DNC).