Minnesotas governor on Sunday called the early morning bombing of a mosque in Bloomington an act of terrorism.

What a terrible, dastardly, cowardly act was committed, Gov. Mark Dayton (D) said during a visit to the Dar al-Farooq Islamic Center. It is a criminal act of terrorism.

The FBI is leading the investigation into the blast that rocked the mosque just after 5 a.m. on Saturday, when a small group of congregants had gathered for morning prayers.

FBI Special Agent Richard Thornton had said on Saturday that a preliminary investigation indicated an improvised explosive device had caused the explosion, and that it remained unclear who was behind the attack.

The Bureau of Alcohol, Tobacco, Firearms and Explosives is also taking part in the investigation.

Bloomington police were called to the Islamic center at 5:05 am on Saturday after reports of an explosion. When officers and fire personnel arrived, what they found there was some smoke, some damage to the building, but no one was injured, Bloomington Police Chief Jeff Potts said at a news conference on Saturday.

Asad Zaman, director of the Muslim American Society of Minnesota, said a witness had seen someone throwing an object at the imams office window from a van or a truck.

Mohamed Omar, the mosques executive director, told reporters a member saw someone leave in a truck shortly after the blast.

One of our congregation members came out immediately and saw a truck fleeing at high speed, Omar said. This is our center. This was our first prayer for the day.

Community members reportedly quelled the flames before first responders arrived.

The Muslim American Society has offered a $10,000 reward for information leading to an arrest and conviction in the bombing.

The Department of Homeland Security said it is in close contact with authorities and community leaders as the investigation proceeds.

The department fully supports the rights of all to freely and safely worship the faith of their choosing and we vigorously condemn such attacks on any religious institution, acting Secretary Elaine Duke said in a news release . We are thankful that there were no injuries, but that does not diminish the serious nature of this act.

So far this year, anti-Muslim marches across the country have led to violence and arrests, and hundreds of Islamophobic incidents have occurred.