Suburban mosque bombed during morning prayers in US state of Minnesota

A mosque in the US state of Minnesota was bombed early on Saturday as worshippers inside prepared for morning prayers, in what is being treated as a possible Islamophobic attack.

The Dar al-Farooq Islamic Center in Bloomington was damaged but no one was injured when the explosive device went off at around 5am in the suburban Minneapolis mosque, Bloomington Police Chief Jeff Potts said.

The FBI has announced it is searching for suspects.

Windows of the imam's office were shattered, either by the blast or by an object thrown through them, the Minneapolis Star Tribune reported.

One worshipper saw a pickup truck speeding away shortly after the explosion, said Mohammed Omar, the centre's executive director.

He said the mosque, which primarily serves people from the area's large Somali community occasionally receives threatening calls and emails.

"We came to this country for the same reason everyone else came here: freedom to worship," Yasir Abdalrahman, a worshipper at the mosque told the newspaper.

"And that freedom is under threat. Every other American should be insulted by this."

Asad Zaman, director of the Muslim American Society of Minnesota, described the attack as a firebombing.

Investigators will try to determine whether the incident was a hate crime and who may have been behind it, according to Richard Thornton, special agent in charge of the FBI's Minneapolis Division.

Thornton said during an afternoon news conference that the explosion was caused by an "improvised explosive device", and that investigators have recovered components of the device to figure out how it was put together.

But he didn't take questions and declined to provide details about the device, citing the ongoing investigation, which is being led by the FBI.

Saturday's bombing comes amid a rise in reports of Islamophobic incidents in the US, including arson attacks and vandalism at mosques, harassment of women wearing hijabs, and bullying of Muslim schoolchildren.

In Minnesota, an Islamic cemetery in Castle Rock Township recently reported it had been vandalised with spray painted profanities and swastikas.

The mosque in Bloomington, just south of Minneapolis, serves as a religious centre and community organising platform for Muslim activists and leaders in the area, according to the society.

The group is offering a $10,000 reward for information that leads to an arrest or conviction.

A $10,000 reward also is being offered by the Minnesota chapter of the Council on American-Islamic Relations, or CAIR. The group said its national office is urging Islamic centres and mosques to step up security.

"If a bias motive is proven, this attack would represent another in a long list of hate incidents targeting Islamic institutions nationwide in recent months," said Amir Malik, the local chapter's civil rights director.

Minnesota is home to the largest Somali community in the US, roughly 57,000 people, according to the latest census figures.

The immigrants have been coming to Minnesota from their war-torn homeland since the 1990s.