Police responded to Cleaver’s Kansas City district office after alarms went off at around 3 a.m. Thursday, FBI spokeswoman Bridget Patton said.
It appeared someone broke an office window with a hammer, then attempted to throw the apparent Molotov cocktails inside, Patton told ABC News. The FBI was investigating the matter as an attempted assault on a federal officer, she added.
The Kansas City Police, the Kansas City Bomb and Arson Squad and the ATF responded, Cleaver’s office said.
"As has been reported, early this morning, a window was broken at Congressman Cleaver's Kansas City, Missouri, office when an individual attempted to throw an item or items at the building," Cleaver’s chief of staff, John Jones, wrote in a statement.
Police found two broken liquor bottles, one for rum and one for Jagermeister, with paper towels sticking out of their necks, the Kansas City Star reported. No staffers were at the office at the time, and no fire damage was reported.
Cleaver was in Washington, and has recently shared national headlines with other Missouri politicians in the wake of the Ferguson shooting. His office noted this was the second incident of vandalism at one of Cleaver’s district offices in the last six years.
Rep. Marcia Fudge, D-Ohio, the chairwoman of the Congressional Black Caucus, condemned the act in a statement, calling it an “attempted arson attack.”
“This type of abhorrent behavior is the most ineffective means of voicing discontent or disagreement,” Fudge said. “I expect a speedy, full and thorough investigation into this incident by law enforcement, so that those responsible are swiftly apprehended and prosecuted.”
All of Cleaver’s offices, including the one vandalized, remained open for regular business, according to a news release.
United States Capitol Police spokesman Shennell Antrobus said the agency was “aware” of the incident, and is working with the FBI and other law enforcement agencies “on this ongoing, active investigation.”
Later in the day, Cleaver released a statement himself, saying, "Today, our thoughts should not dwell on a small incident that hurt no one and caused very minor property damage. Our thoughts and prayers are with the families and friends of those killed on September 11, 2001, and all those who suffered in its aftermath."
ABC's John Parkinson contributed to this report.