Hillary Clinton campaigning in Florida. REUTERS/Brian Snyder

Federal investigators have secured a warrant to examine newly discovered emails related to Hillary Clinton's private server, media outlets reported on Sunday.

The warrant will allow the FBI to examine the emails to see whether they are relevant to its investigation of the private email server used by Clinton, the Democratic presidential nominee, while she was secretary of state from 2009 to 2013.

FBI officials were unavailable for comment on the status of their investigation, according to Reuters.

Clinton's campaign spent Sunday vigorously pushing back against the FBI.

Following Friday's announcement that the bureau discovered emails on former congressman Anthony Weiner's laptop from his estranged wife, Huma Abedin, that passed through Clinton's private server, top Clinton campaign officials fanned out over cable news on Sunday's political talk shows to criticize Comey's decision to publicly announce the renewal of the investigation into Clinton's email.

In an appearance on Fox News on Sunday, Clinton campaign manager Robby Mook said he was "very surprised" by Comey's letter informing congressional leaders of the discovering of potential new emails. Mook said he found the letter "very strange," highlighting reports that the FBI was still awaiting a warrant to review the emails, and argued that reporters were reading too much significance into Comey's ambiguous letter.

"Director Comey has put out a letter," Mook said. "It has three paragraphs. It says nothing about Huma Abedin. It says nothing about who these emails are to or from. It just says that he has information that may be significant — we don't even know it if is."

Other aides argued that the announcement broke with the Department of Justice's guidelines for informing the public about ongoing investigations.

John Podesta, Clinton's campaign chair, on CNN reiterated his concern that Comey was unnecessarily influencing the presidential election without giving voters enough information about the status of the investigation.

"To throw this in the middle of the campaign 11 days out seemed to break with precedent and be inappropriate at this stage," Podesta said.

He added: "He might've taken the first step of actually having looked at them before he did this in the middle of a presidential campaign so close to voting."

Clinton's running mate, Sen. Tim Kaine of Virginia, similarly cited reports that maintained Comey and his team didn't know the contents of the emails before informing Congress and that he overstepped his bounds by making an announcement before he provided clarifying information.

"If he hasn’t seen the emails, they need to make that plain and release the circumstances of those once they have done the analysis," Kaine said on ABC. "That's what Hillary said immediately when she spoke to the press on Friday. She said you can't break both protocols and leave it up in the air with a question mark. You owe people the complete information."

The campaign released a video on social media later on Sunday detailing how initial reporting of the story did not include key information, saying the emails could be duplicates of those the FBI had already revealed. Narrated by press secretary Brian Fallon, the video called Comey's letter "light on facts" and "heavy on innuendo" and suggested that it was further ammunition for Republicans to use against the Democratic presidential nominee.

"The more information that has come out, the more overblown this all seems," Fallon said. "And the more concern it has created about Director Comey's actions."

Later in the video, he added: "Republicans have been trying to use Hillary Clinton's emails to bring her down since the very beginning of this campaign."

Reuters contributed reporting for this article.