US presidential candidate Senator Barack Obama is seen speaking at the California Democratic Party convention in San Diego in this April 28, 2007 file photo. 

Democratic presidential candidate Barack Obama was put under the protection of the US Secret Service on Thursday.

Obama, senator from Illinois, is one of the leading Democratic candidates vying for the party's presidential nomination in the 2008 presidential elections.

Homeland Security Secretary Michael Chertoff, "after consultation with the congressional advisory committee, authorized the United States Secret Service to protect presidential candidate Senator Barack Obama," according to a statement issued by the Secret Service.

The organization did not divulge the reason for the protection.

Another Democratic presidential candidate, Senator Hillary Clinton from New York, already has Secret Service protection because of her husband's former presidency.

The Secret Service, established in 1965, is a federal law enforcement agency mandated by the Congress to protect national and visiting foreign leaders and conduct criminal investigations.

(Xinhua News Agency May 4, 2007)