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Scores more firefighters raced Tuesday to the Okanogan Complex of fires, the biggest wildfire in the history of Washington state and the nation's No. 1 summer wildfire priority. But it still might not be enough.

The complex of five fires near the north-central town of Omak grew by almost 14,000 more acres by Tuesday afternoon, to 258,339 acres, or more than 403 square miles. If it were a city, it would be the 10th-largest in the continental U.S. by area.

"This fire remains the No. 1 priority fire in the United States," said Todd Pechota, chief incident commander for Okanogan Complex.

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Nearly 100 new firefighters arrived at the fire, which has been only 15 percent contained since it started Aug. 15, the joint local-state-federal incident command team said Tuesday. In just 10 days, it has already cost nearly $10 million to battle, commanders said.

Related: Okanogan Complex: Washington Wildfire Is Now Largest in State History

But the fire's northeastward is continuing unabated because, the incident team reported bluntly, of a "lack of resources to implement suppression actions."

Crews were even being diverted from California, even though they're needed there for numerous fires burning hundreds of thousands of acres.

"We've had the opportunity to be on some large fires in California of this magnitude. We expect much of the same that we're used to," said Battalion Chief Mark Brunton, who was leading two California Forestry and Fire Protection crews totaling 44 firefighters to Omak, accompanied by with 10 engines.

"They're very difficult and dynamic incidents," Brunton told NBC station KHQ of Spokane. "We're ready to be here for the long haul."

The Okanogan Complex merged last week with the Twisp River fire, which killed three Washington-based firefighters when their vehicle crashed and was overtaken by flames.

Authorities said Tuesday that a memorial service is planned for Sunday in Wenatchee, Washington, for firefighters Tom Zbyszewski, 20, Richard Wheeler, 31, and Andrew Zajac, 26.

A fourth firefighter, Daniel Lyon, remained critical in intensive care Tuesday at Harborview Medical Center in Seattle, said Susan Gregg, a spokeswoman for the hospital.