The Treasury Department said the GRU and Russia's military both interfered in the 2016 election and were "directly responsible" for the NotPetya cyberattack that hit businesses across Europe in June 2017, causing billions of dollars in damage by disrupting global shipping, trade and medicine production.
The Russian campaign remains lacklustre just three days before the vote, and Mr Putin is overwhelmingly expected to win another term after 18 years in power, riding in part on his argument that he must stand up to Western aggressors.
She said she would pool efforts with Dmitry Gudkov, a former lawmaker and Kremlin critic.
But the USA remained in lockstep with Britain, its closest ally, stressing that it shares the U.K.'s assessment that Russian Federation is to blame, "for the reckless nerve agent attack on a British citizen and his daughter".
Trump has been conspicuous in not condemning Russia - either in his public statements or on his prolific Twitter feed - even after Britain's stern response to the poisoning of Skripal, the 66-year-old Russian ex-spy and his 33-year-old, daughter, Yulia, who fell ill at a shopping center in southern England earlier this month.
"We will always do what is necessary to defend ourselves, our allies and our values against an attack of this sort, which is an attack not only on the United Kingdom, but upon the worldwide rules-based system on which all countries, including Russian Federation, depend for their safety and security", Bristow told reporters.
Speaking on a visit to Salisbury to meet members of the emergency services dealing with the aftermath of the use of the so-called Novichok nerve agent, Mrs May said the statement showed Britain's allies "are standing alongside us".
The Foreign Office says "Russia's response doesn't change the facts of the matter - the attempted assassination of two people on British soil, for which there is no alternative conclusion other than that the Russian State was culpable".
Russian Federation denies being the source of the nerve agent, suggesting it could have been another country, and has demanded Britain share samples collected by investigators.
It said the move was a response to Britain's "provocative actions" and "baseless accusations over the incident in Salisbury on March 4", referring to the poisoning of Sergei and Yulia Skripal with a nerve agent developed in the Soviet Union, which Britain has blamed on Russian Federation.
Russian Federation now faces particular pressure to engage with the Organisation for the Prohibition of Chemical Weapons (OPCW), the body which oversees implementation of the worldwide ban on nerve agents.
He also said he thinks the Skripals, who are in critical condition, have little chance of surviving.
The Russian Ministry of Foreign Affairs said in a statement Saturday that 23 British diplomats are "persona non grata" and must leave the country within a week.
May severed high-level contacts with Moscow and vowed actions against Russian dirty money and "hostile state activity".
He strongly denied Russian responsibility in the March 4 attack.
Britain accused Russian Federation of involvement in the nerve agent poisoning of former double agent Sergei Skripal at a time when London's ties with European partners have been badly strained by Brexit. It prompted threats to shut down RT's British operations, among other actions targeting Moscow.