Arson is being blamed for one of three fires in the past several weeks that charred the historic John H. Stevens House, credited as the birthplace of Minneapolis.

Minneapolis Assistant Fire Chief Melanie Rucker said Tuesday that the Sept. 20 blaze at the Park and Recreation Board's building in the 4900 block of S. Minnehaha Avenue was set by someone who has yet to be apprehended.

"Fire patterns and a positive indication for accelerant indicate that this was [an] intentionally set fire of the exterior of the structure," Rucker said in a statement.

The most recent of the three fires occurred early Saturday, when crews responded shortly before 4 a.m. to find heavy fire rising from a rear corner of the building. Crews cut through a fence and boarding to douse the blaze, which burned the building's first and second floors as well as the roof near the chimney.

Investigative findings into the cause of the weekend fire remain pending, Rucker said.

The building first caught fire on Aug 30. Responding crews found flames on the back side of the building burning through a first-floor wall. The fire was doused before it spread.

Rucker said investigators have classified the cause of this fire as "undetermined."

No injuries were reported in connection with any of the blazes.

The Stevens House was built from 1849 to 1850 on land near where the Minneapolis post office now stands. It soon became a meeting place for early settlers, who went on to found Hennepin County. The city's Park Board took ownership of the house later that century and moved it to Minnehaha Park.