WASHINGTON (REUTERS) - US agencies accused Russia of breaking into government computer networks on Thursday (Oct 23), the second such claim in as many days, while more details emerged of spoofed emails allegedly sent to voters by Iran.

Law enforcement and security agencies have been on high alert to avoid a repeat of 2016, when hackers alleged to be working for Russia's military intelligence stole and released emails belonging to prominent US Democrats in a bid to help President Donald Trump get elected, according to US intelligence agencies, officials, researchers, and experts.

In less than two weeks before the US election on Nov 3, US agencies said that a Russian group, sometimes called Berserk Bear or Dragonfly by researchers, had targeted dozens of state, local, tribal and territorial US governments as well as aviation networks.

The group has previously been observed targeting global critical infrastructure but, in the past two months, the hackers pivoted "to a heavy focus on state and local governments," according to Ms Sarah Jones, an analyst with cybersecurity company FireEye.

In response to a request for comment, the Russian Embassy in Washington pointed to recent comments by Kremlin spokesman Dmitry Peskov calling such allegations "absolutely groundless."

US officials were careful in Thursday's warning - which was posted on the website of the Cybersecurity and Infrastructure Security Agency (CISA), an arm of the Department of Homeland Security - to emphasise that they had no information to indicate the hackers had intentionally disrupted any elections or government operations.

Ms Jones said the hackers instead "seemed to be very interested in collecting large amounts of data, including government records."

US officials said the stolen documents included passwords, security manuals, vendor data and information on how to print access badges.

FireEye, which investigated several intrusions on behalf of clients, said the data did not appear to be election-focused and that there was - so far - no evidence of any effort to damage the networks in question.

"We haven't seen any evidence that they were focused on disruptive or destructive attacks," Ms Jones said.

But the FBI and Department of Homeland Security said the hacking may have had other malign motivations such as laying the groundwork for a future plot.

The scope of the intrusions wasn't fully clear; CISA only mentioned two victims, and their identities were not released.

US Director of National Intelligence John Ratcliffe announced on Wednesday that Russia and Iran had both tried to interfere with the 2020 presidential election, seeking to undermine Americans' confidence in the integrity of the vote and spread misinformation in an attempt to sway its outcome.

Mr Ratcliffe said that Russia obtained voter information and Iran sent spoofed emails to US voters in an attempt to intimidate them.

Few details of the Russian targeting were made public, but Reuters reported that, in the Iranian case, a mistake by the hackers in a video attached to the emails meant that officials were able to identify them almost immediately.

Speaking to CNN, White House Chief of Staff Mark Meadows said that the Iranian emails affected "less than 10,000 people."

"Every person and every vote counts but there's no ballots that are being manipulated," he said. "No tallies that are being manipulated. This was all about trying to sow discord."

Teheran, like Moscow, denied Wednesday's allegations.

The United States on Thursday imposed new sanctions on the Iranian organizations suspected of being involved.

Tension over allegations of foreign interference in the 2020 election is unlikely to dissipate as the contest enters its final stretch.

Some in the Trump administration are still relitigating allegations of foreign meddling in the 2016 vote.

On Thursday Reuters reported that Mr Trump and Mr Ratcliffe have pushed for rapid declassification of a document disputing the 2017 intelligence community finding that the Kremlin worked to help Mr Trump.

The effort faces strong objections from the intelligence community.