LOS ANGELES, Sept. 9 (Xinhua) -- The cost of fighting the largest wildfire in Los Angeles history increased from about 60 million to 70 million U.S. dollars, authorities announced on Wednesday.

    The fire has burned 160,375 acres (about 64,951 hectares) and containment was still listed at 62 percent late Wednesday afternoon, the National Forest Service (NFS) said.

    Full containment, which means building another 19 miles (about 30 kilometers) of fire lines, is expected by Saturday, fire officials said.

    Firefighters had planned on beginning a twice-postponed backfire operation regarded as crucial to protecting the Mount Wilson Observatory, a site of a historic observotary and broadcast towers.

    "They were postponed because the winds started gusting too much," said Jorge Segura of California Fire Department. "If the wind is too strong, you get a fire that goes out of control. It's like throwing gasoline on a bonfire.

    "You have just a small window of opportunity. You have to have the right weather, the right wind, humidity and temperature and obviously the personnel. When you light a fire, you have to be able to control it and have it go where you want it to go," he said.

    The Station Fire raging in the Angeles National Forest since Aug. 25 is slightly more than 250 square miles (400 kilometers), which the NFS described as an area two-and-a-half times the size of Sacramento, capital of California.

    Authorities said the fire was sparked by an arsonist. The state has offered a 100,000-dollar reward for information leading to an arrest and conviction, and the Los Angeles County Board of Supervisors Tuesday authorized a 50,000-dollar reward.

    About 4,500 firefighters are assigned to the blaze, which still threatens 7,000 structures, according to the NFS, the lead agency in the firefighting effort.

    The fire has claimed the lives of two firefighters, injured 13 firefighters and one support worker. It has also destroyed 78 homes, mostly cabins, as well as two commercial properties and 86 outbuildings.

    Investigators said they believed a substance found near the fire's point of origin helped spread the deadly blaze, and it has emerged as a key piece of evidence in the arson probe.

    Sources said investigators are going through a database of arson suspects and fire bugs to search for possible suspects.