Feds say Minnesota mosque explosion caused by IED No one was hurt in the explosion, authorities said.

 -- An explosion on Saturday morning at a mosque in a Minneapolis suburb shattered windows in the imam's office but did not injure anyone, officials said.

The blast rang out at the Dar Al-Farooq Islamic Center in Bloomington around 5 a.m. CDT, when over a dozen people were gathering inside for morning prayers. Although no one was hurt in the explosion, it damaged the imam's office and awoke many residents in the neighborhood, according to Bloomington Police Chief Jeff Potts.

At a press conference Saturday afternoon, Potts said investigators are working to determine the cause of the blast. Preliminary findings indicate it came from a destructive device in violation of federal law, he said.

During an afternoon news conference, Richard Thornton, special agent in charge of the FBI's Minneapolis Division, said the explosion was caused by an "improvised explosive device" and investigators had gathered components of the device and were studying how it was assembled. He provided no further details and didn't take questions, citing the ongoing investigation, which is being led by the FBI.

"At this point our focus is to determine ... you know ... who and why," Thornton said. "It was an improvised explosive device that was set off early this morning."

The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives are involved in the probe.

The Department of Homeland Security issued a statement Saturday evening saying that acting DHS Secretary Elaine Duke is aware and the DHS is "in close contact with federal, state and local authorities and local community leaders as the investigation into this matter continues."

Asad Zaman, director of the Muslim American Society of Minnesota, condemned the explosion at the mosque, which serves as a religious center and community organizing platform for Muslims in the area. Zaman said the blast appears to be a hate crime, and the society is offering a $10,000 reward for information that leads to an arrest or conviction.

The Minnesota chapter of the Council on American-Islamic Relations, or CAIR, was also offering a $10,000 reward.

The Associated Press contributed to this report.