Donald Trump accused his rival Hillary Clinton of being "protected by a rigged system" at the FBI after she was cleared on Sunday night in the scandal around her email practices as secretary of state.

Yet a top Democrat now accuses the Republican's campaign of meddling in the investigation.

"You can't review 650,000 new emails in eight days," said Trump at a rally in a Detroit suburb. "Hillary Clinton is guilty. She knows it, the FBI knows it, the people know it."

Clinton was cleared of any wrongdoing Sunday by FBI director James Comey in a letter to government officials.

FBI employees, Comey said, have been "working around the clock" since he announced 28 October that the federal law enforcement agency was reviewing a batch of emails linked to a closed investigation of Clinton's use of a private server as secretary of state.

"Based on our review, we have not changed our conclusions that we expressed in July," said Comey, referring to his announcement in the summer to close the case without pressing charges.

But Trump said at a rally in Detroit's Sterling Heights neighbourhood that the investigation of Clinton "will go on for a long, long time." He said the "rank and file special agents at the FBI won't let her get away with her terrible crimes," suggesting that dissent within the FBI is being suppressed by Comey.

Last week Trump backer, former New York mayor, Rudy Giuliani, said he heard about this dissent "boiling up in the FBI" against Comey and his decision not to prosecute Clinton. "I can't even repeat the language I heard from the former FBI agents," he said.

Days before Comey's announcement of the review 28 October, Giuliani had hinted that something big was about to happen and that he had advanced knowledge of it.

"There is a problem within the FBI and the New York office appears to have had a direct line into the Trump campaign through Rudy Giuliani," said Christine Pelosi, a political strategist and member of the Democratic National Committee, on BBC's Radio 4's Today programme on Monday 7 November.

She said the Republicans "took advantage of a situation orchestrated by the people who leaked the information." Comey's letter, Pelosi said, "threw the election into chaos" because 20 million Americans cast their ballot in early voting "while that cloud was over our nominee."

Pelosi – who is also the daughter of Democrat and Minority Leader of the United States House of Representatives, Nancy Pelosi – said the FBI's inspector general, who conducts examinations of internal affairs in the bureau, is going to have to look at the facts around any leaks.

"If you're a director of an organization and your agents are leaking to one of the the candidates information about an investigation," she said, "[Comey] really had no choice but to send a letter."

The letter produced a "chaotic situation" in the final days of the election, Pelosi said, because the letter was vague and it was unclear whether Clinton would have to testify again or the investigation reopened.

"People didn't know what his letter meant," she said. "I think it absolutely lost us the opportunity to campaign as effectively as we could have."