WASHINGTON — U.S. officials said that Russian hackers have targeted the networks of dozens of state and local governments in the United States in recent days, stealing data from at least two servers. The warning, less than two weeks before the election, amplified fears of the potential for tampering with the vote and undermining confidence in the results.

The advisory from the FBI and the Department of Homeland Security’s cybersecurity agency describes an onslaught of recent activity by a Russian state-sponsored hacking group against a broad range of networks, some of which were successfully compromised. The alert released Thursday functions as a reminder of Russia’s potent capabilities and ongoing interference in the election even as U.S. officials publicly called out Iran on Wednesday night.

The advisory does not identify by name or location those who were targeted, but officials say they have no information that any election or government operations have been affected or that the integrity of elections data has been compromised.

“However, the actor may be seeking access to obtain future disruption options, to influence U.S. policies and actions, or to delegitimize (state and local) government entities,” the advisory said.

U.S. officials have repeatedly said it would be extremely difficult for hackers to alter vote tallies in a meaningful way, but they have warned about other methods of interference that could disrupt the election, including cyberattacks on networks meant to impede the voting process. The interference could continue during or after the tallying of ballots if Russians produce spoofed websites or fake content meant to confuse voters about election results and lead them to doubt the legitimacy of the outcome.

A broad concern, particularly at the local government level, has been that hackers could infiltrate a county network and then work their way over to election-related systems unless certain defenses, such as firewalls, are in place. This is especially true for smaller counties that don’t have as much money and IT support as their bigger counterparts to fund security upgrades.

On Thursday, the Treasury Department Announced Sanctions Against Five Iranian Entities

Officials have nonetheless sought to stress the integrity of the vote, with FBI Director Christopher Wray saying Wednesday, “You should be confident that your vote counts. Early, unverified claims to the contrary should be viewed with a healthy dose of skepticism.”

On Thursday, Chris Krebs, the head of Homeland Security’s Cybersecurity and Infrastructure Security Agency, said officials don’t have reason to believe that hackers were looking for election infrastructure or election-related information, and aren’t aware of any activity “that would allow them to come anywhere near a vote.” He said the alert was issued in regard to the scanning of county networks for vulnerabilities, not specifically to the targeting of elections.

“The election-related risk is the fact that they were in or touching an election system,” he said.

The threat from the Kremlin was mentioned but not especially emphasized during a hastily called news conference on Wednesday night, when officials said Russia and Iran had obtained voting registration information — though such data is sometimes easily accessible. But most of the focus was on Iran, which officials linked to a series of menacing but fake emails that purported to be from a far-right group and were aimed at intimidating voters in multiple battleground states.

John Ratcliffe, the director of national intelligence, said the operation was aimed at harming President Donald Trump, though he didn’t elaborate on how.

On Thursday, the Treasury Department announced sanctions against five Iranian entities, including the Islamic Revolutionary Guard Corps, for attempting to influence U.S. elections.

Despite Iran’s activities, Russia is widely regarded in the cybersecurity community as the bigger threat to the election. The U.S. has said that Russia, which interfered in the 2016 election by hacking Democratic email accounts and through a covert social media effort, is interfering again this year in part through a concerted effort to denigrate Trump’s Democratic opponent, Joe Biden.

U.S. officials attribute the recent activity to a state-sponsored hacking group variously known as DragonFly and Energetic Bear in the cybersecurity community. The group appears to have been in operation since at least 2011 and is known to have engaged in cyberespionage on energy companies and power grid operators in the U.S. and Europe, as well as on defense and aviation companies. Aviation networks are among the entities that officials say were recently targeted, according to Thursday’s advisory.

As of October 1, the Advisory Said, the Hackers Have Exfiltrated Data From at Least Two Servers

According to the advisory, the hackers have obtained user and administrator credentials to enter the networks and moved laterally inside to locate what they felt would be “high-value” information to steal. In at least one breach, officials say, the hackers accessed documents related to network configurations and passwords, IT instructions and vendors and purchasing information.

As of October 1, the advisory said, the hackers have exfiltrated data from at least two servers.

John Hultquist, the director of threat intelligence at FireEye, said Energetic Bear moved to the top of his worry list when the cybersecurity firm observed it breaking into state and local governments in the U.S. that administer elections, due to it having targeted election systems in 2019.

Hultquist said he does not think Energetic Bear has the ability to directly affect the U.S. vote but fears it could disrupt local and state government networks proximate to the systems that process votes.

“The disruption may have little effect on the outcome. It may be entirely insignificant to the outcome — but it could be perceived as proof that the election outcome is in question,” he said. “Just by getting access to these systems they may be preying on fears of the insecurity of the election.”