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The fire burned about 3.7 square miles (9.6 square kilometers) and was only about 20% contained Thursday afternoon as firefighters used water-carrying helicopters to douse hot spots and bulldozers to dig containment lines, the Texas A&M Forest Service said.

Investigators believed the fire was started Wednesday by what was supposed to be a controlled burn on private property, said Josh Mizrany, assistant chief law enforcement officer with the Texas A&M Forest Service.

Investigators will look into how the fire spread, he said, and evidence could be turned over to local prosecutors if necessary.

Officials had not reported widespread damage or any injuries. Montgomery County officials said they knew of one home that burned to the ground.

The Cleveland Independent School District, which has about 12,000 students, canceled classes as a precaution.

Florida fires

a large brush fire that began Tuesday caused authorities to close the two roads leading in and out of the island chain, because of smoky conditions and to allow firefighters to move equipment.

Officials said the fire had burned about 34 square miles (88 square kilometers) and was about 20% contained.

Spring break is in full swing in Florida, and officials said U.S. 1, the major thoroughfare that connects the mainland to the islands, was expected to have intermittent closures in the coming days. It is also a heavily traveled road for people who live on the mainland and work at many of the hotels and restaurants in Key Largo and beyond.

Arkansas blazes

In Arkansas, crews responded to nearly than 100 fires Wednesday that were fueled by high winds and were dealing with five new ones Thursday.

The fires closed several highways, including a portion of Interstate 530 southeast of Little Rock due to heavy smoke.

Flames damaged structures in several cities, including Little Rock. The roof collapsed at St. Joseph’s, a 115-year-old building in North Little Rock that once served as an orphanage and is now the home of a nonprofit that provides urban farming resources.

What's causing the fires?

The South has experienced recent cold and dry conditions, followed by gusting winds, that have fanned the flames.

Texas has seen fire hazards range from the far northern Panhandle, where ground vegetation froze and dried out, and push hundreds of miles east to the coast.

South Florida has seen every little rainfall over the past few weeks. The rainy season doesn't start until sometime around mid-May. Another cold front with dry air is expected to push through South Florida on Thursday night, said meteorologist Donal Harrigan with the ºÃÉ«tv Weather Service in Miami.

Red Flag warnings

The weather service issued Red Flag warnings for fire conditions in east Texas and South Florida and could extend them for several days.

Red flag warnings are issued by the ºÃÉ«tv Weather Service when conditions are ripe for fires. In southeast Texas, weather service officials predicted wind gusts of 25 miles per hour (40 kilometers per hour), combined with humidity as low as 18%. That combination will continue to dry out vegetation.

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Frisaro reported from Fort Lauderdale, Florida, and DeMillo reported from Little Rock, Arkansas.