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Cain will receive Secret Service protection

This post has been updated.

Republican presidential candidate will begin receiving protection from the Secret Service at his campaign's request, NBC's Kelly O'Donnell reported Thursday.

Cain will be the first Republican presidential candidate to begin receiving protection after having applied for a detail with Homeland Security Secretary Janet Napolitano.

Sources tell NBC News the Secret Service protection for Herman Cain begins at 8pm tonight. Those involved in the evaluation for using taxpayer dollars this way determined that "there's clearly some credible threats."

Officials will not say whether a specific incident or concern prompted the authorization.

It's not clear what circumstances contributed to Cain's protection; the service will not say when the detail will begin or whether any specific concerns prompted this step.

Cain had previously been protected by a private detail. That private detail came under scrutiny Thursday for its interaction with a reporter. Texas Gov. Rick Perry receives protection through the Texas state police, and Minnesota Rep. Michele Bachmann's private security had also previously prompted reporter complaints.