Georgian officials believe a grenade was thrown at the stage where President Bush (search) was giving a speech Tuesday, prompting the U.S. Secret Service to investigate what could have been a deadly security breach.

The Secret Service learned of the possible grenade after Bush left the former Soviet republic on Tuesday. Georgian authorities said a device was thrown within 100 feet of the stage before knocking against a spectator and falling to the ground, according to Secret Service spokesman Jonathan Cherry.

The report stated that a Georgian security officer picked up the device and removed it from the area. The Secret Service had not seen the device as of Tuesday evening, Cherry said. It has agents in Tbilisi working with the FBI, State Department and Georgian authorities to investigate the report.

"Anytime there's a report of this nature, of course we take it very seriously," Secret Service spokesman Jim Mackin told FOX News.

Guram Donadze, spokesman for the Georgian Interior Ministry, said no hand grenade was thrown close to Bush. "This is an absolute lie. This did not occur," Donadze told The Associated Press.

Officials from President Maikhail Saakashvili's (search) office were not immediately available for comment. Georgia's security service has been merged with the Interior Ministry.

The White House referred the AP to the Secret Service for comment.

Cherry said he couldn't characterize the source of the report that a device had been thrown.

Bush returned to the United States Tuesday after a four-country trip that also included stops in Russia, Latvia and the Netherlands. He was the first American president to visit Georgia.

The Associated Press contributed to this report.