WASHINGTON (AP) -- Herman Cain on Thursday became the first Republican presidential candidate to receive Secret Service protection.

Cain asked for the security and Homeland Security Secretary Janet Napolitano and congressional leaders approved his request Thursday, Secret Service spokesman Ed Donovan confirmed.

There have been threats against Cain, who had been experiencing a bounce in the polls, according to an official with knowledge of the situation who asked not to be identified because of the sensitive nature of the situation. The nature of the threats was unclear.

Donovan would not say whether there had been any threats or discuss why protection was being provided.

The campaign confirmed in an email early Friday that Cain was receiving federal protection.

"Due to the recent surge in the polls and the large crowds of enthusiastic supporters at recent campaign events, we are appreciative of the extra level of protection provided by these elite professionals," the Cain campaign said in a statement.

While it's unknown whether a specific incident triggered the request, police reports show that Cain's campaign has been the target of a threatening phone call on at least one occasion.

On June 1, Cain's campaign office in Stockbridge, Ga., reported receiving a call from someone who did not identify himself but who claimed to be a member of the Ku Klux Klan. The man said that Cain, who is black, should not run for the White House.

"Tell him not to run" and "there's no such thing as a black Republican," the man said, according to a written statement Cain's administrative assistant, Lisa Reichert, gave to the police. The caller did not explicitly threaten violence.

The Associated Press obtained a copy of the police reports using Georgia's open records law.

Local police alerted the FBI and the U.S. Secret Service to the incident.

Secret Service protection is given to each major party's presidential nominee but can be provided earlier if the Homeland Security Department approves a campaign's request.

When then-Sen. Barack Obama was placed under Secret Service protection in May 2007, it was the earliest ever for a presidential candidate. One of his rivals, Hillary Rodham Clinton, already had a protective detail because she was a former first lady.

In the 2004 campaign, Democratic candidates John Kerry and John Edwards received their protection in February of that year as they competed for the party's nomination.

Federal law allows candidates to seek protection if they meet a series of standards, including public prominence as measured by polls and fundraising.

Napolitano consulted Thursday with a congressional advisory committee made up of the House speaker, the House and Senate majority and minority leaders and the House sergeant-at-arms, the chief law enforcement officer in the House.

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Associated Press writer Ray Henry in Atlanta contributed to this report.

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