Department of Homeland Security Secretary Michael Chertoff authorized Obama's protection after consultations with the bipartisan congressional advisory committee, according to Chertoff spokesman Russ Knocke and the Secret Service.
Secret Service spokesman Eric Zahren would not provide details of what led to the extra security, but said, "I'm not aware it was based on any threat." According to the Department of Homeland Security, there were no known threats and Obama requested the protection.
Obama campaign officials will not say why they requested early protection, reports CBS News correspondent Bob Orr. But one source inside the campaign said there is concern about the size of Obama's crowds, and the crush of people who want to press close or even touch a candidate who exudes rock star appeal.
Obama's rival, Sen. Hillary Rodham Clinton, has a Secret Service detail that is provided to all former first ladies.
The agency and the department would not comment on the scope of Obama's protection or provide any other security details. Obama's campaign did not immediately respond to questions about the extra security.
In the last election, Democratic candidates John Kerry and John Edwards received their protection in February 2004 as they were competing for the party's nomination. Obama's detail comes nine months before the first votes are cast.
Federal law allows candidates to seek protection if they meet a series of standards, including public prominence as measured by polls and fundraising. The members of the congressional advisory committee are the Speaker, the House and Senate majority and minority leaders as well as one additional member.
In a February interview with 60 Minutes' Steve Kroft, Obama's wife, Michelle, addressed the possibility that her husband could be the target of an assassination attempt. "I don't lose sleep over it because the realities are that, you know, as a black man, you know, Barack can get shot going to the gas station, you know," she said. "So you can't make decisions based on fear and the possibility of what might happen. We just weren't raised that way."
In a Feb. 12 interview with The Associated Press, Obama dismissed concerns about his own security, but would not answer directly when asked if he had received death threats. The Rev. Jesse Jackson drew early Secret Service protection because of violent threats during his campaigns for president in the 1980s.
"I face the same security issues as anybody," the Illinois senator told the AP. "We're comfortable with the steps we have taken."