"The US Intelligence Community (USIC) is confident that the Russian Government directed the recent compromises of e-mails from US persons and institutions, including from US political organisations," said a joint statement issued by the Department of Homeland Security and Director of National Intelligence.
The recent disclosures of alleged hacked e-mails on sites like DCLeaks.com and WikiLeaks and by the Guccifer 2.0 online persona are consistent with the methods and motivations of Russian-directed efforts, it alleged.
"These thefts and disclosures are intended to interfere with the US election process," the US statement said.
Such activity is not new to Moscow the Russians have used similar tactics and techniques across Europe and Eurasia, for example, to influence public opinion there, it alleged.
"We believe, based on the scope and sensitivity of these efforts, that only Russia's senior-most officials could have authorised these activities," the statement said.
However, in Moscow the Kremlin labelled allegations by the US that the Russian government was behind the hacking of American political organisations as "rubbish".
"This is again some sort of rubbish," Kremlin spokesman Dmitry Peskov told Russian news agency Interfax.
"Every day (President Vladimir) 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."
Some states have also recently seen scanning and probing of their election-related systems, which in most cases originated from servers operated by a Russian company, the US Government alleged.
"However, we are not now in a position to attribute this activity to the Russian Government," it said, adding that as per their assessment it would be extremely difficult for someone, including a nation-state actor, to alter actual ballot counts or election results by cyber-attack or intrusion.
This assessment is based on the decentralised nature of US election system in this country and the number of protections state and local election officials have in place.
"States ensure that voting machines are not connected to the Internet, and there are numerous checks and balances as well as extensive oversight at multiple levels built into our election process," it said.
As such, the Department of Homeland Security has convened an Election Infrastructure Cybersecurity Working Group with experts across all levels of government to raise awareness of cyber security risks potentially affecting election infrastructure and the elections process.