A hand grenade was found near US President George Bush during his visit to Georgia, security officials say.
Tens of thousands listened to Mr Bush's speech in Tbilisi
Georgian officials say the hand grenade was inactive and therefore did not pose any danger to either President Bush or Georgian President Mikhail Saakashvili.
It was found 30m (100 feet) away from where Mr Bush had been addressing a huge crowd in Tbilisi's Freedom Square.
The US Secret Service said it had been told of Tuesday's incident after Mr Bush had left the ex-Soviet republic.
Georgia's security chief said there was no chance that the Soviet-made RPG-5 hand grenade could have exploded and that the intention was probably to create public fear.
"The goal is clear - to frighten or to scare people and to attract the attention of the mass media," Gela Bezhuashvili told reporters.
"In any case there was no danger whatsoever for the presidents."
The US Secret Service confirmed they were investigating the matter.
"It was reported that a device hit an individual in the crowd and the device fell to the ground," Secret Service spokesman Jonathan Cherry said.
"At this time we have not seen the reported device," he said.
"We have agents on the ground in Tbilisi working with the FBI, State Department and host-country security authority to look further into this report."
Mr Bush's speech was the centrepiece of his visit to Georgia - the first by a US president.
Security had been tight in the square with a heavy police presence, US snipers were visible on rooftops and American agents manned security gates.
John Barletta, a secret service agent for former US President Ronald Reagan, told the BBC's World Today programme that providing security for presidents was an increasing challenge.
"Now you are looking for other things - for terrorist activities, someone could put a missile in there, now you are looking for aircraft that could explode into a crowd," he said.
"The secret services assigned to protect the president have widened their circle drastically."
During his speech Mr Bush praised President Mikhail Saakashvili and told the tens of thousands of people gathered that Georgia's 2003 Rose Revolution had been an inspiration to people everywhere.
"You gathered here armed with nothing but roses and the power of your convictions and you claimed your liberty," the US president said.
In a reference seen as being directed at Russia, Mr Bush said all nations must accept the territorial integrity of Georgia, where separatists in two breakaway regions - Abkhazia and South Ossetia - have aligned themselves with Moscow.
Mr Saakashvili boycotted Monday's World War II commemorations in Moscow in protest at Russia's continued presence.