At least 18 classified emails from an account belonging to Huma Abedin have been found by the FBI on the top Hillary Clinton aide's estranged husband Anthony Weiner's laptop, a conservative group claims.

Five previously unreleased classified emails were among 147 documents released by the State Department last week, conservative watchdog group Judicial Watch said on Thursday.

'It wasn't just low-level classified materials that were found in the Clinton email server,' Judicial Watch President Tom Fitton told Fox News' Tucker Carlson Tonight on Thursday.

Five previously unreleased classified emails were among 147 documents released by the State Department last week, conservative watchdog group Judicial Watch president Tom Fitton (pictured) said on Thursday

The emails were found on an account belonging to top Hillary Clinton aide Huma Abedin on a laptop belonging to her estranged husband Anthony Weiner

Watch the latest video at <a href="http://www.foxnews.com">foxnews.com</a>

He added: 'There were highly top secret documents of the most secure type and it would have resulted in a criminal prosecution, I guarantee you, if you were anyone else but the Democratic nominee for president.'

It was unclear whether the emails were deemed classified at the time they were sent or when the State Department was preparing them for release.

Fitton said: 'These are classified records that [Former FBI Director] James Comey and his colleagues... knew were on the Weiner laptop, but didn't take seriously enough to pursue criminal charges against Abedin or Clinton for allowing this egregious abuse of trust that the American people placed in them.'

The State Department said it 'carefully reviews the content of records requested through FOIA to determine whether any information is sensitive or classified,' and some of the documents released Friday have 'classified information that has been redacted.'

The FBI found thousands of emails exchanged between Clinton and Abedin while searching Weiner's laptop.

The FBI found thousands of emails exchanged between Clinton and Abedin (pictured together above) while searching Weiner's laptop

Former FBI Director Jim Comey has said the FBI had concluded that neither Weiner nor Abedin had committed a crime in their handling of the email

The search came after the FBI launched an investigation into Weiner's sexting with a high school student, which was revealed by DailyMail.com in 2016.

The discovery of the emails led then-FBI Director James Comey to announce in late October 2016, as Clinton's run for the White House was in its final stage, that he was reopening the probe of her use of a private computer server.

Then two days before Election Day, the FBI declared there was nothing new in the emails. Clinton has called Comey's intervention 'the determining factor' in her defeat.

The FBI has since said that only a small number of the emails found on the laptop had been forwarded while most had simply been backed up from electronic devices, including most of the email chains containing classified information.

Comey said the FBI had concluded that neither Weiner nor Abedin had committed a crime in their handling of the email.

Weiner started a 21-month sentence in December after being convicted of sexting a 15-year-old girl.

Abedin announced last year that she was divorcing Weiner, with whom she has a six-year-old son.