WASHINGTON (AP) — FBI Director James Comey says there have been additional “attempted intrusions” into voter registration databases beyond what was previously known, and that the agency is looking “very, very hard” at Russian hackers who may try to disrupt the U.S. election.

Comey’s comments come amid ongoing concern about the ability of hackers from Russia or other nations to breach voting systems. The FBI last month warned state election officials to boost their security in light of evidence that hackers targeted related data systems in at least two states, Illinois and Arizona.

Comey did not say where the intrusions were or give any additional details.

At a separate congressional hearing Wednesday, a Homeland Security official attempted to assuage concerns, saying the government has confidence in the integrity of the U.S. electoral system.

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