Fire investigators say a wildfire that destroyed 11 homes in Karlstad, Minn. last week was probably arson.

The Department of Natural Resources says the fire is still being investigated, and a $6,000 reward is being offered for information that helps identify the person who set it.

Curt Cogan,DNR forestry program coordinator who is managing the investigation for the DNR, said the suspicion is based on evidence found at the origin of what became known as the County 27 fire, rather than witnesses or calls from the public. Investigators have simply ruled out other causes, such as lightning, a passing train, or working farm equipment, said Kittson County Sheriff Kenny Hultgren.

"When you have no known cause other than somebody lighting it, that's when you have arson," Hultgren said.

It was one of at least eight fires that blazed across the extremely dry, flat and grassy landscape of northwest Minnesota in extremely windy conditions last week. Cogan said it's possible some of the other fires might also have been set.

The County 27 fire started at 2 p.m. Sept. 30, a Sunday, at the intersection of Kittson County Hwy. 27 and 250th Av. NW, about 5 miles southwest of Karlstad. By Monday it had grown to 500 acres, and ultimately burned 4,440 acres, forcing a partial evaucation of the city of Karlstad.

Hultgren said many of the arson wildfires in Kittson County begin on Sunday afternoons.

Why?

"I have no idea," he said.

"We're going to work this one vigorously," he added.

Hundreds of firefighters are still working across the region, including 180 on the 4,400-acre North Minnie fire, north of Red Lake, which Wednesday was 35 percent contained. Gil Knight, spokesman for the interagency team working on that fire, said it's been difficult to get firefighters and equipment to the fire's north side, which is in an area with few roads.

Also, the North Minne fire, as well as the Viking fire, near Thief River Falls, have dropped below ground into a layer of peat. Peat fires burn in low oxygen conditions without flame, can move laterally underground and are hard to put out. Officials have indicated they could burn for months.