Stunned FBI agents who uncovered thousands of Hillary Clinton emails while examining Anthony Weiner's electronic devices for explicit messages he sent to a 15-year-old girl described the discovery as an 'oh s**t' moment, a new book claims.

A technician tasked with rifling through Weiner's iPad, iPhone and laptop in September 2016 found 340,000 emails between the Secretary of State and her top aide Huma Abedin, Weiner's estranged wife, with many using a hillaryclinton.com address.

The investigation into Weiner's devices began when DailyMail.com revealed that the disgraced congressman had an online sexual relationship with the troubled teenager for months and sent her lewd messages and pictures.

One agent in the FBI team compared the discovery of Clinton's use of a private email server to 'dropping a bomb in the middle of the meeting', James B. Stewart writes in his new book Deep State: Trump, the FBI, and the Rule of Law.

But the shocking discovery went ignored at the FBI because senior officials were 'overwhelmed' by the investigation into Russian meddling in the 2016 election, Stewart wrote.

Nobody at Quantico was taking action, so one agent went outside the chain of command and shared the allegations with New York prosecutors, which led to James Comey reopening the investigation days before the 2016 election.

Stunned FBI agents who uncovered thousands of Hillary Clinton emails while examining Anthony Weiner's electronic devices for explicit messages with a 15-year-old girl (right) described the discovery as an 'oh s**t' moment, a new book claims

According to the book, Weiner's iPad, iPhone and laptop unveiled 340,000 emails between Hillary Clinton and her top aide Huma Abedin, Weiner's estranged wife, many using a hillaryclinton.com address

One agent was 'scared' by the damning emails he found and then 'pressed on his superiors to follow up on the bombshell discovery'.

Deep State says that the new emails that were found on Weiner's devices by a lowly but determined FBI case officer.

'I'm telling you that we have potentially ten times the volume that Director Comey said we had on the record,' the agent told Stewart. 'Why isn't anybody here?'

James B. Stewart's new book Deep State: Trump, the FBI, and the Rule of Law is out today

Stewart also reveals that former Comey had deep concerns about the impartiality of former Attorney General Loretta Lynch.

When it came to the investigation into Hillary Clinton's use of a private email server, Comey considered asking for her to appoint a Special Counsel because he was so alarmed - but she rebuffed him.

Weiner was given 21 months in prison for sending sexually-explicit texts to the underage girl. He was released after 18 months and is believed to have moved back in with Abedin.

The girl was pictured but never identified. Weiner was aware that the girl was underage, according to DailyMail.com interviews with the girl and her father, as well as a cache of online messages.

He asked her to dress up in 'school-girl' outfits for him on a video messaging app and pressed her to engage in 'rape fantasies'.

Deep State also claims that FBI lawyer Lisa Page, who was caught sending anti-Donald Trump texts, lied about her affair with FBI agent Peter Strzok when the director of the bureau confronted her.

Page told Andrew McCabe that she and Strzok were not an item and had never been romantically involved.

Page was 'acutely embarrassed, mortified' that her affair was public but chose to lie rather than tell the truth, Stewart writes in the book.

When their relationship did become public, so did the texts they exchanged mocking Trump and his supporters, with the two becoming a symbol of the so-called Deep State that was out to get the President.

Weiner carried on a months-long sexual relationship with a 15-year-old girl online, and even sent her photos of himself, including one of him in a pool

In one message, he tells the girl he was 'hard' after thinking of her that morning

In another message, both Weiner and the girl tell each other they feel like they can tell each other anything. The pair even joke about nicknames for each other, and Weiners old name of 'Carlos Danger.' But he says he wants her call her 'mine'

The relationship between Page and Strzok has become a lightning rod for Trump and his allies who see it as evidence of bias in the investigation into Russian interference.

Strzok worked on Special Counsel Robert Mueller's investigation but his texts to Page appeared to show a bias, such as discussing an 'insurance policy' if Trump won the 2016 election.

Strzok also called Trump an 'idiot' and after he won wrote to Page: 'OMG I am so depressed'.

In one Confide message - which deletes the sender's name after the first message is open, Weiner tells the girl 'I would bust that tight p***y. 'The app is designed for confidentiality, and automatically deletes messages and images after the first time they are read or viewed. However, the girl took photos of a few of the messages and images from last February and March, which she shared with the Dailymail.com.

He goes on to say that he would 'bust' it 'so hard and so often that you would be limp for a week'

'I have repeatedly demonstrated terrible judgement about the people I have communicated with online and the things I have sent,' Weiner told DailyMail.com at the time

Stewart also reveals that former FBI director James Comey had deep concerns about the impartiality of former Attorney General Loretta Lynch. When it came to the investigation into Hillary Clinton's use of a private email server, Comey considered asking for her to appoint a Special Counsel because he was so alarmed - but she rebuffed him

FBI lawyer Lisa Page lied to Andrew McCabe about her relationship with agent Peter Strzok (right), new book Deep State: Trump, the FBI, and the Rule of Law claims. Strzok, who worked on Robert Mueller's probe, was caught calling Trump an 'idiot' and discussing an 'insurance policy' if Trump won the 2016 election

In the online messages the FBI was looking into, Weiner sent bare-chested photos of himself to the underage girl, repeatedly called her 'baby' and complimented her body, and told her that he woke up 'hard' after thinking about her, according to copies of the conversations.

In one lewd message, he told the teen: 'I would bust that tight p***y so hard and so often that you would leak and limp for a week.'

When confronted with the claims, Weiner did not deny exchanging 'flirtatious' messages with the teen. He declined to comment on the specifics of the allegations on the record, but provided copies of two emails the girl sent him that he contends raised questions about her claims. DailyMail.com publishes them below.

He gave a statement to DailyMail.com at the time in which he said, in part: 'I have repeatedly demonstrated terrible judgement about the people I have communicated with online and the things I have sent. I am filled with regret and heartbroken for those I have hurt.'

Weiner has faced a number of sexting scandals since 2011, when he was forced to resign from Congress after his online sexual messages with a female college student were revealed.

Another sexting scandal in 2013, involving 22-year-old Sydney Leathers, derailed his bid for New York City mayor. In the course of that scandal, his alias Carlos Danger was disclosed.