A DHS official said that a request came from the candidate but would not say anything about the reason for the protection or the nature of any threat(s).
Homeland Security Secretary Michael Chertoff authorized Obama's protection after consultations with the congressional advisory committee, according to department spokesman Russ Knocke.
Secret Service Spokesman Darrin Blackford said the congressional advisory committee currently is comprised of Chertoff, House Speaker Nancy Pelosi, House Minority Leader John Boehner, Senate Majority Leader Harry Reid, Senate Minority Leader Mitch McConnell and one additional member selected by the others but not necessarily a member of Congress.
Obama's campaign will not elaborate on specific details, but FOX News has learned that the request did not emerge from a singular reason, but a combination of considerations, including the logistical and security concerns associated with Obama's attending two 20,000-plus person rallies in recent weeks and his rising popularity. Obama's being a high-profile African-American running for the presidency was also taken into consideration before for the formal request was made.
The request also emerged from a more generalized type of concern raised by comments written on fringe Web logs and sites, but not a specific threat, FOX News has learned.
Secret Service spokesman Eric Zahren would not provide details of what led to the extra security, but said he was not aware of it being "based on any threat."
“Security has been implemented,’ Zahren told FOXNews.com without providing specifics into why the order for a detail was implemented or how many agents are assigned to the Illinois senator.
It's the earliest security assignment for a candidate in a presidential campaign. Usually protection is not provided until a party chooses its nominee, however, Sen. Hillary Clinton, another Democratic candidate, has Secret Service detail because she is a former first lady.
FOX News' Carl Cameron, Corbett Riner and Melissa Drosjack contributed to this report.