Representatives of the Federal Bureau of Investigation (FBI) and Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are participating in the investigation.
"We are thankful that there were no injuries, but that does not diminish the serious nature of this act," the statement said.
No reports regarding the reasons of the incident have emerged so far.
Media reported citing witnesses that an improvised explosive device could be thrown to the mosque through a window. Asad Zaman, executive director of the Muslim American Society of Minnesota, said that the imam's window was broken and that the bomb could be thrown from a vehicle, according to CNN.
The authorities announced a $10,000 reward for the information, which may help to find the perpetrators, according to the broadcaster.