An "improvised explosive device" targeting a mosque in Minneapolis during morning prayers on Saturday damaged the imam's office, but did not cause any injuries, the Federal Bureau of Investigation (FBI) said.

According to a report on the Minneapolis Star Tribune, someone apparently threw the bomb through a window that caused the explosion at the Dar Al-Farooq Islamic Center in Bloomington town, south of Minneapolis city.

The blast at 5:00am damaged the imam's office but worshippers managed to put out the fire, even before the firefighters arrived at the scene, the report said quoting a statement from the Muslim American Society of Minnesota. The FBI is leading the investigating.

Several mosques and American Muslims have come under attack amid a wave of Islamophobia triggered by statements by some of the Republican candidates during the 2016 presidential campaign, including United States (US) President Trump who had proposed a complete ban on Muslims from entering the US.

Following up on his election promises, and after several legal challenges, President Trump was eventually able to get a decision in support of his Executive Order that ban citizens from six Muslim-majority countries from travelling to the US for at least 90 days, allowing authorities to implant a stricter screening process.

The attack on the Dar-Al-Farooq Islamic Centre is the latest in a string of attacks that took place during and after the presidential election campaign.

Asad Zaman, the society's director said that a witness reported something being thrown at the imam's office when about a dozen people had gathered for morning prayers.

Another witness saw a pickup truck speeding away after the blast. The blast was loud enough to be heard across the street.

Mohammad Omar, the center's executive director, said that the mosque, which serves people from the area's large Somali community, occasionally received threatening calls and email.

"We came to this country for the same reason everyone else came here: freedom to worship, and that freedom is under threat. Every other American should be insulted by this," Yasir Abdalrahman, a worshipper, told Politico magazine.

The Islamic society has offered $10,000 as a reward for information that can help track the suspect.

The Minnesota chapter of another Muslim group, the Council on American-Islamic Relations or CAIR, is also offering an award of $10,000.