The Trump campaign has denounced the message and distanced itself from what it described as a "horrible statement" made by Trump's longtime former butler 84-year-old Anthony Senecal.
Senecal worked as Trump's butler for 17 years before being named the in-house historian at the tycoon's Mar-a-Lago estate in Palm Beach, Florida.
The Secret Service, which has the responsibility to protect the US President and his family, said it would investigate the matter.
In a message posted on Facebook, Senecal, 84, expressed profound hatred for President Barack Obama and declared he should be killed, according to Mother Jones magazine which first reported the massage.
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The message could only be read by Senecal's friends and is not public. A picture of the message was posted by Mother Jones in its news report yesterday.
"I wrote that (Facebook message). I believe that," Senecal was quoted as saying by Mother Jones.
"To all my friends on FB, just a short note to you on our pus headed "president" !!!! This character who I refer to as zero (0) should have been taken out by our military and shot as an enemy agent in his first term !!!!!," Senecal said in his Facebook post.
The hate message was immediately condemned by the Trump Campaign.
"Tony Senecal has not worked at Mar-a-Lago for years, but nevertheless we totally and completely disavow the horrible statements made by him regarding the President," a Trump campaign spokesman said in a statement, according to ABC News.
According to news reports, Senecal has written anti-Obama hate messages in the past also. There was no immediate response from the White House.