The FBI has spent the past year investigating the Clinton Foundation over claims they were trading access for donations to the charity, leading to friction between the bureau and the Justice Department.

Agents in New York and Little Rock have been leading the probe, but have been ordered by senior officials in Washington and the Justice Department to scale back the extent of the probe due to a lack of evidence.

The row emerged over the weekend in the aftermath of the decision by FBI Director James Comey to announce the bureau has reopened its investigation into Hillary Clinton's email server - less than a fortnight before the election.

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Hillary Clinton's presidential campaign has been thrown into chaos new allegations over her emails, this time contained on a laptop owned by Anthony Weiner, the estranged husband of her longterm aide Huma Abedin, left, who was investigated by the FBI over a sexting scandal

Abedin's husband Anthony Weiner, pictured, was investigated by the FBI over allegations that he had sexted a 15-year-old girl. It is understood that the FBI has found emails on Weiner's computer which relate to Abedin's work with Clinton at the State Department

Clinton, pictured, has denied any wrongdoing and is continuing on the campaign trail

Last February, according to the Wall Street Journal, the FBI updated the Justice Department on its investigation into the Clinton Foundation.

But officials at Justice did not believe the FBI had found any significant evidence of corruption that would warrant continued investigation.

However, when Director Comey decided in July that Hillary Clinton's use of a private email server did not warrant prosecution, FBI agents in New York restarted their probe into the Clinton Foundation.

By August, there was increased tension when the Justice Department learned about the continued FBI investigation.

Officials in Washington feared the probe so close to November's election could be viewed as political interference.

However, Donald Trump, pictured, said he never thought he would ever thank Anthony Weiner and claimed the latest email scandal proves that his opponent is not worthy of being president

Trump's campaign has been revitalized by the new scandal involving a Clinton aide

FBI Director James Comey has faced criticism over the timing of his announcement with claims that he has directly interfered with next month's presidential election

FBI agents in New York wanted access to laptops surrendered by two of Clinton's former staff under the terms of a plea agreement to search the machines for evidence relating to their charity investigation.

However, this access was denied as the plea agreements only extended to emails directly relating to possible national security issues.

It is understood the agents in New York had already had access to a computer owned by former New York congressman Anthony Weiner, who is the estranged husband of Clinton's longtime aide Huma Abedin.

Agents had seized Weiner's computers as part of a separate probe into allegations he had sexted an underage girl.

During the examination of his laptop, the FBI found emails which they claimed required further investigation.

Director Comey announced the new investigation last week much to the delight of Clinton's Republican challenger Donald Trump.

Clinton, pictured, has seen her massive poll lead over Trump collapse since the latest scandal

The FBI wants to review the emails to see if they contain classified information and were handled properly, the focus of the earlier Clinton inquiry.

Separately Sunday, another law enforcement official said FBI investigators in the Weiner sexting probe knew for weeks about the existence of the emails potentially related to the probe of Clinton's server.

A third law enforcement official also said the FBI was aware for a period of time about the emails before Comey was briefed, but wasn't more specific.

In his letter that enraged Democrats , Comey said he'd been briefed on Thursday about the Abedin emails and had agreed that investigators should take steps to review them.

It was not immediately clear Sunday what steps investigators took once the emails were first found to fully advise FBI leaders that additional and potentially relevant messages had been discovered.

The timing of Comey's letter less than two weeks before Election Day drew criticism from Democrats and some Republicans who cast it as unprecedented and as potentially tipping the scales in the presidential race in favor of Republican Donald Trump.

Energized by the news, the GOP presidential nominee has rallied his supporters, calling the latest developments worse than Watergate and arguing that his candidacy has the momentum in the final days of the race.

Donald Trump said in Nevada following the revelations: 'We never thought we were going to say "thank you" to Anthony Weiner.'

Trump also highlighted reports that the Justice Department had discouraged the FBI from alerting Congress to the unexpected discovery of the emails, and said the department is trying 'so hard' to protect Clinton.

Comey told FBI colleagues in a memo Friday that he was aware the letter to Congress was at risk of being misunderstood, but he said he felt obligated to notify lawmakers about the new emails after having told them that the matter was closed.

Dozens of former federal prosecutors, including former Attorney General Eric Holder, have signed a letter critical of Comey's decision. And Senate Minority Leader Harry Reid wrote to Comey saying the action may have violated the law.

Clinton's use of a private email server while secretary of State has dogged her campaign since early last year. In July, Comey recommended against criminal prosecution after a months-long investigation, but rebuked Clinton and her aides for being careless with classified material.

Justice Department officials who were advised of the FBI's intention to notify Congress about the discovery expressed concern that the action would be inconsistent with department protocols designed to avoid the appearance of interference in an election. Comey acted independently when he sent several members of Congress a letter about the emails on Friday, said one of the officials.

It was not immediately clear what the Abedin emails were about or what significance, if any, they carried to the Clinton email server investigation.