The Federal Bureau of Investigation is looking into a possible attempt to bomb the office of a Missouri congressman early Thursday morning, when a window was broken and devices resembling Molotov cocktails hurled at the building, an official said, according to The Associated Press.

Police in Kansas City responded at about 3 a.m. local time to the local office of U.S. Rep. Emanuel Cleaver and found that a window had been broken with a hammer, said Bridget Patton, spokeswoman for the FBI in Kansas City, the AP reported.

Two Molotov cocktails appeared to have been thrown at the building but ended up on the ground without causing a fire or other damage, Patton said, though the hammer went through the window, according to the AP.

The bottles used in the attempted firebombing, one rum and one Jagermeister, were found on the ground after police were called to Cleaver's office around 2:50 a.m., Kansas City Police Sgt. Kari Thompson said, the AP reported.

No staff members were in the building in central Kansas City at the time and Cleaver was in Washington, his chief of staff, John Jones, said in a statement, the AP reported.

"Folks, my staff is safe and law enforcement is investigating," Cleaver, a Democrat, said in a Twitter posting, according to the AP. The FBI was investigating because it has jurisdiction in cases of attempted assaults on federal officers, including members of Congress, Patton said. Kansas City police were also investigating, she said.

Jones said this was the second time in six years that someone has thrown items at the building, the AP reported.

"This is the second incident within the last six years," Jones, Cleaver's chief of staff, said in a statement, according to the AP. "The Kansas City Police have completed their initial survey of the scene and we await their report."