A thumb drive and a server containing copies of emails Hillary Clinton sent and received while US secretary of state will be handed over to the FBI, media reports said on Tuesday.
Clinton has been criticized for her decision to use a personal email server while secretary of state, and the Federal Bureau of Investigation has recently begun looking into the possibility that Clinton sent and received classified information from the server.
"It is her hope that State and the other agencies involved in the review process will sort out as quickly as possible which emails are appropriate to release to the public, and that the release will be as timely and transparent as possible," Clinton campaign spokesman Nick Merrill told CBS News.
"She directed her team to give her email server that was used during her tenure as Secretary to the Department of Justice, as well as a thumb drive containing copies of her emails already provided to the State Department."
Last month, the inspector general of the US intelligence community found that four emails sent through that server -- in a sample of 40 of the 30,000 emails provided by Clinton -- contained information that was classified when they were sent.
Earlier Tuesday, the inspector general's office sent a letter to Senator Charles Grassley, head of the US Senate's Judiciary Committee, informing him that it had determined two of those four emails were, in fact, highly classified -- meaning the information they contained was more secret than originally thought.
This determination appeared to trigger the handing over of the emails to the FBI Tuesday.
Clinton, frontrunner for the Democratic presidential nomination in 2016, has said she handled email through her personal servers for convenience.
Critics have painted the private email server as a way to keep critical information out of the public record.
"It may have been convenient for her, but it has been troubling at multiple levels for the rest of the country," US Representative Trey Gowdy, head of the Select Committee on Benghazi, said in a statement.
The committee is investigating the 2012 Benghazi attacks and has taken interest in emails about the incident that may be on Clinton's server.
"Secretary Clinton's decision to prioritize her own convenience - and desire for control - over the security of our country's intelligence should concern all people of good conscience," Republican Gowdy said.
The State Department has disputed whether the emails in question were classified at the time they were sent.
"Department employees circulated these emails on unclassified systems in 2009 and 2011 and ultimately some were forwarded to Secretary Clinton. They were not marked as classified," State Department spokesman John Kirby said Tuesday.
The thumb drive -- also known as a USB flash drive -- had been in the possession of Clinton's attorney, David Kendall.
It was turned over to the FBI after the agency determined he could not keep the classified information they are thought to contain, according to US media reports.
The server has previously been reported to have been wiped clean by Clinton.