Democratic presidential hopeful Hillary Clinton has agreed to hand over her private email server and a collection of work-related emails to the US Justice Department.

Ms Clinton was criticised when it emerged earlier this year that she used her private email account linked to an internet server in her home in New York for work when she was secretary of state.

Her opponents have accused her of side-stepping laws surrounding transparency and record-keeping.

For months, Republican politicians have demanded that Ms Clinton relinquish the server for inspection by an independent party, which she said she was not willing to do.

The Federal Bureau of Investigation recently began looking into the security of the federal records and classified information contained among Ms Clinton's emails.

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.

Mr McCullough has said he found at least four emails in a sample of 40 Clinton emails 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 government forbids the sending of classified information outside unsecured networks because it could harm US national security if intercepted.

The statement from Nick Merrill, a Clinton campaign spokesman, suggested the hardware was being handed over as part of the FBI inquiry.

It remained unclear whether this was in response to a government request, or even came as the result of a subpoena.

"She pledged to cooperate with the government's security inquiry, and if there are more questions, we will continue to address them," Mr Merrill said in the statement. He declined to provide further details.

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 under President Barack Obama, Ms Clinton eschewed an official state.govemail address in favour of a private email account run from a home computer server.

At least one senior aide, Huma Abedin, also used the server for some work email.

Ms 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 politicians and the public to which they are entitled, critics say.