Democratic presidential candidate Hillary Clinton is giving the US Justice Department her private e-mail server and a thumb drive of work-related e-mails from her tenure as secretary of state, a spokesman for her campaign said on Tuesday.

Clinton's use of her private e-mail for her work as America's top diplomat came to light in March and drew fire from political opponents who accused her of sidestepping transparency and record-keeping laws.

The private account was linked to a server in her New York home. For months, Republican lawmakers have demanded that Clinton relinquish the server for inspection by an independent party, which Clinton said she was not willing to do. Some of those lawmakers quickly began issuing statements on Tuesday night, saying their concerns were vindicated as not being motivated only by politics.

The Justice Department and the Federal Bureau of Investigation both declined to comment.

The FBI recently began looking into the security of the federal records and classified information contained among Clinton's e-mails. The US government considers federal records to be government property.

The Justice Department has said the FBI began investigating after the inspector general who oversees the US intelligence agencies, I. Charles McCullough III, formally notified them of his concern that there was classified information not in the government's control.

McCullough has said he found at least four e-mails in a sample of 40 Clinton e-mails he was allowed to inspect contained information that was classified at the time it was sent, including two that contained information deemed "top secret," the highest classification level.

The FBI has declined to give details about the nature of its investigation and who it might encompass, although it is likely to prove an unwelcome distraction for Clinton for months as she tries to keep voters focused on her policy proposals.

Throughout her four years as secretary of state, Clinton eschewed an official state.gov e-mail address in favor of a private clintonemail.com e-mail account run from a home computer server. At least one senior aide, Huma Abedin, also used the server for some work e-mail.

Clinton said the unusual arrangement broke no rules that were in force at the time, although the arrangement has caused long delays in providing federal records to lawmakers and the public to which they are entitled, critics say.

Trey Gowdy, the Republican chair of a US House of Representatives committee investigating the killing of four Americans at a US diplomatic building in Benghazi, Libya, has said his work has been hampered in this way.

"This is a serious national security issue, and the seriousness of it should transcend normal, partisan politics," Gowdy said in a statement on Tuesday.

Last December, Clinton provided what she said were copies of all the work e-mails she had in her possession, nearly two years after she stepped down as secretary of state.

Clinton handed over about 30,000 e-mails she sent and received, although her staff have since acknowledged without explanation that some work e-mails are missing. She did not hand over another 30,000 e-mails from this period that she deemed personal and said she chose "not to keep."