A United States Forest Service employee has been arrested and charged with starting one of the wildfires that have been raging in Colorado for more than a week.

Forestry technician Terry Barton, 38, faces charges of setting fire to timber in a national forest, damaging government property, and making false statements to investigators.

Ms Barton changed her original story - that she found an illegal camp fire - saying a fire that she had started herself to burn a personal letter had got out of control.

She is scheduled to make an initial court appearance in a Denver federal court on Monday.

"This is one of the hardest announcements I've had to make in my career," said Forest Service official Rick Cables as he told a news conference of her arrest.

The forest fires, which have consumed some 40,000 hectares (100,000 acres) and forced several thousand people from their homes, have been described as the worst in the state's history.

Ms Barton admitted starting a blaze while patrolling the Hayman area of Pike National Forest to enforce a fire ban, US federal prosecutor Bill Leone said.

She said she had decided to burn a letter from her estranged husband which had upset her.

She set fire to it in an authorised camp fire site and then left believing she had extinguished the fire, she said.

But driving past the site after turning round her vehicle she found that the fire had spread beyond the camp fire ring. She tried but was unable to suppress the fire.

If convicted, Ms Barton could be sentenced up to 10 years in prison and fines of up to $250,000.

Hot weather forecast

Firefighters have gained ground on the fires that have burned within 65 kilometres (40 miles) of Denver, the Associated Press reports.

With higher humidity and calmer winds, officials are hoping the flames will not spread too much further.

But the fires may not be fully extinguished until September, and long-term weather forecasts also indicate further hot weather.

Last week, a state of emergency was declared by the Colorado governor - an action which enables the state to activate the National Guard and call on federal resources if needed.

The fires have also blackened parts of California, Arizona and New Mexico.

The cost of fighting the blazes has been estimated at around $20m.