Kremlin rejects allegations while senior US administration official says action will be taken against Russia to protect interests "at a time and place of own choosing."
The US government for the first time on Friday formally accused Russia of a campaign of cyber attacks against Democratic Party organisations ahead of the November 8 presidential election.
"We believe, based on the scope and sensitivity of these efforts, that only Russia's senior-most officials could have authorised these activities," a US government statement said on Friday about hacking of political groups.
"These thefts and disclosures are intended to interfere with the US election process," the statement said.
US intelligence officials concluded weeks ago that the Russian government was conducting or orchestrating cyber attacks against the Democratic National Committee and the Democratic Congressional Campaign Committee, possibly to disrupt or discredit the election, in which Democrat Hillary Clinton faces Republican Donald Trump.
The Kremlin on Friday labelled allegations by the United States that the Russian government was behind the hacking of American political organisations "rubbish".
"This is again some sort of rubbish," Kremlin spokesman Dmitry Peskov told Russian news agency Interfax.
"Every day Putin's website gets attacked by several tens of thousand of hackers. A lot of these attacks are traced to the territory of the USA, but we do not blame the White House or Langley each time."
Kerry calls for war crimes investigation of Russia and the US says Russia was behind election hacks. Happy birthday, Putin!— Christopher Miller (@ChristopherJM) October 7, 2016
The Obama administration's decision to blame Russia for the attacks is the latest downward turn in Washington's relations with Moscow, which are under strain over Russia's actions in Syria and Ukraine and in cyberspace.
I applaud the Administration's decision to publicly name Russia as the source of hacks into U.S. political institutions.— Adam Schiff (@RepAdamSchiff) October 7, 2016
Also on Friday, US Secretary of State John Kerry said Russian and Syrian actions in the Syrian civil war, including bombings of hospitals, "beg for" a war crimes investigation.
I wonder if we can now get a proper Magnitsky list since the U.S. is now accusing Russia of war crimes and hacking https://t.co/mAPdSSNLig— Bill Browder (@Billbrowder) October 7, 2016
In addition, a US intelligence official said Friday that Russia is moving short-range nuclear-capable missiles into Kaliningrad, a tiny Russian enclave between Poland and Lithuania, confirming Estonian news reports.
Change in tone
Still, until Friday, the administration had avoided publicly naming Russia in connection with the mounting civilian deaths in Syria or the cyber attacks.
The statement by the Department of Homeland Security and the Office of the Director of National Intelligence did not blame the Russian government for hacking attempts against state election systems, but said "scanning and probing" of those systems originated in most cases from servers operated by a Russian company.
However, a Department of Homeland Security spokesman told Reuters that US officials have concluded that the hacking attacks or probes of state voter registration systems are "consistent with Russian motivations."
Read between the leaks; People didn't pick candidates with a clean history. Democrats didn't, Republicans didn't.— Anonymous (@YourAnonNews) October 7, 2016
Concern has grown about the reliability of the US voting system as a result of the breach, and Republican presidential candidate Donald Trump has called the system "rigged," but without providing specific evidence.
US intelligence officials have said there is no evidence that voting recording systems have been manipulated.
Naming Russia as the actor behind the cyber attacks on political organisations falls short of more punitive measures the United States has taken against other countries for cyber intrusions.
Republican Senator Cory Gardner, chairman of the US Senate Foreign Relations Subcommittee on East Asia, the Pacific and International Cybersecurity, said he planned to introduce sanctions legislation.
Earlier this year, a US grand jury indicted seven Iranians employed by two Iran-based computer companies on hacking charges into US financial sector.
In 2015, Obama announced sanctions against North Korea for hacking into Sony Pictures. In 2014, the United States charged five Chinese military hackers for economic espionage aimed at US nuclear, metals and solar industries.
A senior US official said the administration is considering other retaliatory steps against Russia, but he declined to identify them. Those steps may remain covert, the official said.
"We will take action to protect our interests, including in cyberspace, and we will do so at a time and place of our choosing," another senior administration official told said, echoing language usually reserved for military campaigns.
"The public should not assume that they will necessarily know what actions have been taken or what actions we will take."
The Democratic National Committee publicly disclosed intrusions into its systems in June, blaming Russia for the attacks.
Leaks of the committees' emails from pro-transparency group WikiLeaks soon followed, demonstrating what appeared to be favoritism for Clinton over another Democrat, Bernie Sanders, by committee chairwoman Debbie Wasserman Schultz. Wasserman Schultz, a Florida congresswoman, stepped down.
In Friday's statement, the government said disclosures of emails by WikiLeaks and hacking entities known as DCLeaks and Guccifer 2.0 "are consistent with the methods and motivations of Russian-directed efforts."
WikiLeaks has not identified the source of its leaks and criticised those who have claimed it was Russia.
Guccifer 2.0 has identified itself as a Romanian hacker, but US intelligence officials have concluded it and DCLeaks are both a front for Russian spy units.