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State investigators are taking the lead in a probe to find the cause of a "fire and explosion" that prompted evacuations along the University of Minnesota campus last week.

Minneapolis fire officials were called Thursday to a report of a fire in the basement of the three-story Delta Tau Delta fraternity house on University Avenue SE. City Fire Chief Bryan Tyner said it seems gasoline in the sewer system caught fire and blew several manhole covers along the main thoroughfare near campus.

On Saturday, the Minnesota State Fire Marshal's Office announced it would serve as the lead agency in the investigation. The office said staff from multiple agencies worked "overnight and into Saturday morning" and "have not found additional evidence of odors or high levels of flammable materials while monitoring the system."

"At this time, we think the situation has stabilized, but we remain vigilant," Fire Marshal Jim Smith said in the statement.

The Fire Marshal's Office said it is working with the Metropolitan Council's Environmental Services division and fire departments in Minneapolis and St. Paul and will continue to monitor the systems over the next few days.

"We also continue to investigate to find the source that is responsible for the discharge of a hazardous material into the system," Smith said.