About 1.7 million customers in 10 states and the District of Columbia remained without power Tuesday, four days after storms swept across the mid-Atlantic area. Crews from as far away as Canada, Texas and Wyoming raced to remove fallen trees and restore power so customers from Indiana to Delaware would have lights, refrigeration and air-conditioning, as relentless heat gripped much of the eastern United States. The total without power early Tuesday included about 410,000 in West Virginia, 400,000 in Ohio and 340,000 in Virginia. Authorities said some customers would not have electricity until the weekend. \"While I want to thank them for their progress, they need to move faster,\" Washington Mayor Vincent Gray told CNN. More than 43,000 customers in Washington were without power early Tuesday. Temperatures were forecast to reach 98 degrees Fahrenheit, with a 75 percent chance of thunderstorms in the afternoon. The 911 emergency phone service in Fairfax County, Va., outside Washington operated at half capacity as Verizon\'s primary and backup power systems failed after Friday night\'s storm, leaving much of northern Virginia with no 911 service through the weekend. Fairfax County is home of the CIA and four other top US intelligence agencies. AT&T, Sprint, T-Mobile and Verizon said they were trying to get generators to sites that lost power, The Washington Post reported. Virginia, Washington, DC, Maryland, West Virginia and Ohio declared states of emergency because of damage from the widespread, violent storm that brought hurricane-force winds across 700 miles from the Midwestern United States to the Atlantic seaboard. The National Weather Service described Friday\'s storm system as a derecho, a widespread, long-lasting storm associated with a fast-moving band of severe thunderstorms in the form of a squall line. Derechos occur mostly in summer, especially June and July in the Northern Hemisphere, and can strike, as this storm did, at night as well as in the daylight hours. At least 18 people were killed from Ohio to New Jersey, while another three people died in fresh storms in North Carolina Sunday. Severe thunderstorms with strong winds and hail ripped through north-central Minnesota Monday, knocking out phone service in Bemidji, a city between Duluth and Grand Forks, in the state of North Dakota. Storms also struck parts of southern Illinois, Kentucky and Tennessee, the National Weather Service said.