Leaders of a Minnesota mosque that was bombed have called on Donald Trump to condemn the incident that has been labelled an “act of terrorism”.

Dar Al-Farooq Islamic Centre's director Mohamed Omar urged the US President to acknowledge the attack, which happened just before morning prayers on Saturday in Bloomington.

Governor Mark Dayton called the bombing “an act of terrorism” but Mr Trump has yet to make a public statement on the incident.

Officials say witnesses saw someone throw something from a truck or van before the blast and saw a vehicle speed away afterward. The FBI believe it was an “improvised explosive device”.

Nobody was hurt in the explosion, but the blast damaged the imam's office across the hall from the worship space.

“We invite the president to come and see — to come and see what happened,” Mr Omar told BuzzFeed News.

“He is the president of this country, and this happened to us. He has to come here and at least express his feelings and say this is bad.”

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Director of the Muslim American Society of Minnesota Asad Zaman also urged Mr Trump to recognise the attack.

“We are wondering why President Trump has not tweeted about this. He seems to want to tweet about security and terror issues,” he said.

Mr Omar said the mosque did not have security cameras fitted to the outside of the building because the community, which is made up mostly of Somali immigrants, couldn’t afford them.

He also said the mosque didn't receive any threats beforehand or claims of responsibility afterward.

The Minneapolis FBI office has not announced arrests or said whether it has identified any suspects.

In a statement Monday afternoon, Special Agent in Charge Rick Thornton called it a "terrible crime" and vowed to focus every available resource on the case until it's solved.

He also said certain questions could not be answered due to the ongoing investigation.

"I want to assure the community that this investigation is our top priority and we continue to work to determine who carried out this crime and why," he said. "These are important questions, and it will take time to develop the information necessary to answer them."

Mr Omar said the bombing had been "horrific and tragic," but added: “On the other hand, good people came out, and they outnumber that one bad guy, and we are so pleased and so happy to see this community coming together in our support."