BOISE — The nation's wildfire preparedness was officially raised to its highest level as dozens of new fires broke out in the bone-dry West, including a rapidly growing blaze that closed part of the Idaho National Laboratory, a sprawling complex for nuclear research in the southeastern Idaho desert.

The preparedness level had been at level four for only a few weeks when officials, worried about overtaxed crews and resources, decided to raise it to level five, effective Thursday.

The change allows fire managers to request help from additional international crews, including from Canada and Australia, and soldiers with National Guard units could be mobilized. About 15,000 U.S. firefighters already were battling nearly 70 fires bigger than 100 acres in 12 states.

"It's driven by a couple of things: The number of large fires we have, and also the fires are occurring in several states and in several geographic areas," said Randy Eardley, spokesman for the National Interagency Fire Center here. "The resources we have are being stretched thin."

Dry lightning started dozens of new blazes in Idaho, Nevada, Oregon and Utah. Since Monday, there have been more than 1,000 new fires reported across the West, Eardley said.

The fire that started Wednesday evening on the INL grounds quickly swept across nearly 15 square miles or 9,500 acres of sagebrush and grassland on the southeast side of the 890-square-mile nuclear research area. Its cause was not known, said John Epperson, an INL spokesman.

No INL facilities were in immediate danger, but 700 employees of the lab's Materials and Fuels Complex were told to stay home Thursday.

The fire had burned within a mile of U.S. Highway 20, forcing the closure of part of the road for much of the night. By Thursday morning, the highway had reopened, Idaho State Police said, and the blaze was about 10 percent contained.

The Materials and Fuels Complex, about five miles northeast of the edge of the fire and on the far side of the highway, conducts research into nuclear reactor fuels, said INL spokesman Ethan Huffman.

He said the metal-roofed complex was surrounded by vast sand buffers and the wildfire posed no danger to it, but operations were suspended. Other facilities at INL, which employs about 3,600 workers, remained open.

National Interagency Fire Center spokesman Ken Frederick said Thursday that no international crews had been brought in yet, but new crews were arriving in the Pacific Northwest from Alaska and the southeastern U.S.