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The FBI obtained a warrant to search emails related to the probe of Hillary Clinton's private server that were discovered on ex-congressman Anthony Weiner's laptop, law enforcement officials confirmed Sunday.

The warrant came two days after FBI Director James Comey revealed the existence of the emails, which law enforcement sources said were linked to Weiner's estranged wife, top Clinton aide Huma Abedin. The sources said Abedin used the same laptop to send thousands of emails to Clinton.

The FBI already had a warrant to search Weiner's laptop, but that only applied to evidence of his allegedly illicit communications with an underage girl.

Agents will now compare the latest batch of messages with those that have already been investigated to determine whether any classified information was sent from Clinton's server.

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Comey's disclosure included few details about what the emails contained. In a letter to Congress, he said the FBI learned "of the existence of e-mails that appear to be pertinent" to the Clinton probe, but he added that the agency "cannot yet assess whether or not this material may be significant."

The revelation ignited fierce criticism. Citing the longstanding practice of avoiding even the appearance of acting in a manner that could tip the political scales, former Justice Department spokesman Matt Miller said that "most people, when they hear that the FBI is involved, automatically assume the negative."

Related: Trump Gives a Grateful Shout Out to ... Anthony Weiner

Clinton called the move an "unprecedented" departure from FBI policy, and on Sunday, Senate Democratic leader Harry Reid scolded Comey for potentially breaking the law.

"Your actions in recent months have demonstrated a disturbing double standard for the treatment of sensitive information, with what appears to be clear intent to aid one political party over another," the letter says. "I am writing to inform you that my office has determined that these actions may violate the Hatch Act."

The act bars government officials from using their authority to influence elections.

Reid also accused Comey of shielding Republican presidential nominee Donald Trump from scrutiny over his connections to Russia, saying "it has become clear that you possess explosive information about close ties and coordination" between Trump and his advisers and the Russian government.

Related: Trump Says He Doubts U.S. Intel Officials on Russian Hacking

The FBI didn't immediately respond to requests for comment on Reid's letter. Earlier, Comey said in an internal message to FBI employees that "we don't ordinarily tell Congress about ongoing investigations, but here I feel an obligation to do so given that I testified repeatedly in recent months that our investigation was completed."

The note added that it would "be misleading to the American people were we not to supplement the record. At the same time, however, given that we don't know the significance of this newly discovered collection of e-mails, I don't want to create a misleading impression."