Investigators are still working to determine the causes of the three most recent fires in Sioux Falls.

Fire Marshal Dean Lanier says the investigations continue into the fires Monday night at 111 North Cleveland Avenue, Tuesday morning at 4506 West 12th Street, and Tuesday evening at 904 North Wayland.

The North Cleveland Avenue fire in the first-floor hallway of a three-story apartment building has been called "suspicious." But Lanier says the cause isn't known and he can't talk about the origin:

Lanier says around 150 fires are reported in an average year in Sioux Falls, and he says despite the recent rash of fires, the numbers are generally staying flat for 2014. He also says the three recent fires were not connected, and the residents of the building on North cleveland Avenue have not yet been able to return to their homes.