Shannon Rowland, the state fire marshal's spokeswoman, said agents found four ignition points for a huge wildfire between Edmond and Guthrie in central Oklahoma that consumed 2,000 acres and destroyed 31 homes and 100 out-buildings before it was put out.
State agents also blamed arson for a still-raging fire that already has devoured 5,500 acres and 30 structures in LeFlore County in eastern Oklahoma, along the Arkansas border.
All told, firefighters have battled more than 100 wildfires across Oklahoma this week, including a massive blaze in the Arbuckle Mountains about halfway between Dallas and Oklahoma City that has scorched more than 34,000 acres and destroyed several houses, cabins and other structures.
"There are a number of fires that have been set," Ms. Rowland said. "Whether they were all intentionally set or not we don't know yet."
In Caddo County, authorities jailed Joshua D. East, 18, of Anadarko on arson charges for another fire. Police allege he set a fire on Sept. 11 that ignited a parched field west of Anadarko. That blaze was extinguished before doing any serious damage.
Also Thursday, Gov. Frank Keating added charcoal and gas grilling to the state's ban on outdoor burning.
"We are under deadly conditions and there is no excuse for careless behavior by our citizens," he said in a prepared statement. "I encourage law enforcement officials statewide to strictly enforce the burn ban."
State officials said it is too early to establish an overall damage estimate, but crop losses already are believed to be about $7 million.
Crews â€“ including about 300 U.S. Forest Service firefighters from throughout the South â€“ hoped to take advantage of Thursday's cooler temperatures and lighter winds to gain an upper hand over fires that remained out of control in the Arbuckle Mountains of southern Oklahoma, in Osage County in northeastern Oklahoma and in LeFlore County.
"If they can whip them today and this evening, we'll be in pretty good shape," said National Weather Service meteorologist Kevin Brown.
In the Arbuckles, where the largest area of wildfires was burning, three National Guard helicopters continued dousing the wildfires with water.
On the ground, firefighters worked to contain the flames by focusing on the northeast corner, near the YMCA's Camp Classen, and southwest corner, near the Mountain Lake and Woodford residential areas.
Ms. Rowland, the state fire marshal's spokeswoman, said agents investigating the wildfires between Edmond and Guthrie found evidence of fireworks that could have ignited grass, brush and timber left bone dry by central Oklahoma's 53 days without measurable rain.
"Whether or not the fireworks were a factor in this, we don't know," she said. "They may have been left over from the Fourth of July holiday."
Ms. Rowland said authorities are searching for two vehicles that were seen in the areas where the fires started: a blue minivan with gold trim across the bottom, bright shiny hubcaps and Texas license plates and an older car with square tail lights, one of which was burned out. A young white man with blond hair was seen in the minivan, she said.
The Associated Press contributed to this report.