A federal law enforcement official told the New York Times that the hack appears to have come from Russia.

"An analytics data program maintained by the DNC, and used by our campaign and a number of other entities, was accessed as part of the DNC hack," Clinton press secretary Nick Merrill said in a statement. "Our campaign computer system has been under review by outside cyber security experts. To date, they have found no evidence that our internal systems have been compromised.”

The news comes hours after the Democratic Congressional Campaign Committee (DCCC) confirmed it was hacked as well.

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The DCCC called its intrusion “similar” to the attack on the Democratic National Committee (DNC), which led to Wikileaks publishing tens of thousands of internal emails.

The trove’s release led to the resignation of DNC Chairwoman Debbie Wasserman Schultz earlier this week.

The Department of Justice is investigating the cyberattacks, Reuters reported. Those with knowledge of the investigation told the news service that involvement was a sign the White House believed the attacks were state-sponsored.

Reuters reported Thursday that the FBI had opened an investigation into a digital intrusion at the DCCC.

"The FBI is aware of media reporting on cyber intrusions involving multiple political entities and is working to determine the accuracy, nature and scope of these matters," a spokesperson said. "The cyber threat environment continues to evolve as cyber actors target all sectors and their data. The FBI takes seriously any allegations of intrusions and we will continue to hold accountable those who pose a threat in cyberspace." The FBI did not directly confirm the hack in a statement to Buzzfeed News, but acknowledged that it is looking into allegations.

Many in the U.S. intelligence community believe hackers linked to the Russian government were behind the DNC hack, but Director of National Intelligence James Clapper cautioned on Thursday against jumping to conclusions.

“I don’t think we’re quite ready yet to make a call on attribution,” Clapper said at the Aspen Security Forum. “We all know there’s just a few usual suspects out there, but in terms of the process we try to stick to, I don’t think we’re ready to make a public call on that yet.”

Democrats have blasted Trump for the comments, accusing him of encouraging foreign intelligence agencies to meddle in America's affairs by attacking Clinton.

Updated at 6:49 p.m.