An overnight blast hit the premises of the U.S. embassy in Kiev but there were no casualties, Ukrainian police said on Thursday.
The explosion hit the mission located in central Kiev shortly after midnight, a statement said.
"Investigators found that an unknown person threw an explosive device on the territory of the diplomatic mission," it said.
The U.S. embassy was not immediately contactable for comment but a diplomat, speaking on condition of anonymity, told AFP: "The embassy will continue to function normally."
The authorities are investigating the incident as a suspected act of terrorism.
The conflict in eastern Ukraine between the government and pro-Russian separatists has caused many weapons to come into circulation.
Weapons are confiscated and people are injured by careless use of weaponry on an almost daily basis.