Secret Service agents are investigating the details of a Facebook poll that asked users whether the president should be assassinated.

The survey -- "Should Obama be killed?" -- was posted by an independent third-party user on Saturday. Facebook administrators removed the poll immediately after learning of its existence, and soon after blocked the person responsible from using the social networking Web site.

"We are aware of it and we will take the appropriate investigative steps," Darrin Blackford, a Secret Service spokesman, told the the Associated Press on Monday. "We take all of these things seriously."

UPDATE: 6:51 p.m. -- Facebook spokesman Barry Schnitt told CNN in an interview that Facebook users first brought the suspicious poll to the Web site administrators' attention.

"As is usually the case, our vigilant users reported it to us first," he said. "The [Secret Service] sent us an e-mail late this morning PDT asking us to take it down. At that point, it had already been removed and we let them know."

He added: "[The application] was immediately suspended while the inappropriate content could be removed by the developer and until such time as the developer institutes better procedures to monitor their user-generated content."