* Record temperatures expected from St. Louis to Washington
* Utilities working to restore power after weekend storms
July 2 (Reuters) - Relentless heat was forecast for much of the eastern United States for a fourth straight day on Monday, after violent storms killed at least 15 people and knocked out power to more than 3 million customers.
"Hot and hotter will continue to be the story from the plains to the Atlantic Coast for the next few days," the National Weather Service said.
Emergencies were declared in Maryland, Ohio, Virginia, West Virginia and Washington, D.C., during the weekend because of damage from storms that unleashed hurricane-force winds across a 500-mile (800-kilometre) stretch of the mid-Atlantic region.
Almost 2.4 million people from Illinois to Virginia were still without power Monday morning, with the biggest concentration of outages in the Washington, D.C. area.
The storms came as sweltering temperatures topped 100 Fahrenheit (38 Celsius) in several southern cities, including Atlanta, where the mercury hit an all-time record of 106 degrees (41 C) on Saturday and reached 105 on Sunday.
Over two-dozen cities across 10 states set or tied all-time record high temperatures on Friday and Saturday, including Columbia, South Carolina; Knoxville, Tennessee; and Raleigh, North Carolina.
One of the hardest hit cities was Charlotte, North Carolina, where the mercury reached 104 degrees (40 C) on Sunday.
From St. Louis, Missouri, to Washington, D.C., temperatures were forecast to hit more all-time records on Monday.
Excessive heat warnings and advisories continued on Monday over much of the mid-Mississippi Valley and southern states, and temperatures were forecast to remain well above normal for a large portion of the United States.
Strong to severe thunderstorms were possible across the southern mid-Atlantic region and north-central United States, the National Weather Service said.
Thunderstorms and high winds battered eastern North Carolina on Sunday afternoon, leading to three more deaths on top of at least 12 caused by deadly storms in several states on Saturday.
In Pitt County near Greenville, a man was killed when his shed fell on him as he tried to put his golf cart inside, said David Glenn of the National Weather Service.
A couple was killed in neighboring Beaufort County when a tree fell on their golf cart, he said.
More than 40 people were reported injured in Beaufort County and numerous homes were damaged in Pitt County, said Christy Wallace, spokeswoman for the Pitt County sheriff.
After power outages that affected some 15,000 customers, Greenville Utilities said Monday morning that all major outages had been repaired.
Powerful storms that brought wind gusts of up to 90 mph (145 kph) on Sunday knocked out power to more than 200,000 Commonwealth Edison customers in northeastern Illinois and about 100,000 remained without power on Monday, the utility said.
Power crews worked on Monday to restore service to homes and businesses, and officials in some areas said the job could take up to a week. Utilities in Ohio, Virginia and Maryland described damage to their power grids as catastrophic.
FirstEnergy utilities had restored service on Sunday to more than 314,000 of the 566,000 customers affected by the storm. The company said it expected to restore power to its Maryland, Ohio and Pennsylvania customers by Tuesday and Wednesday, but it could be late in the week before power is restored to all its customers in West Virginia.
Pepco, which serves Washington and much of its surrounding suburbs in Maryland and Virginia, reported about 233,000 without power on Monday morning. Baltimore Gas & Electric said about 235,000 customers remained without power, but it had restored electricity to more than 400,000.
Storms killed six people in Virginia and left more than 1 million customers without power. Two people were killed in Maryland, officials said.
A falling tree killed two cousins, aged 2 and 7, in New Jersey and heat was blamed for the deaths of two brothers, ages 3 and 5, in Tennessee who had been playing outside in 105-degree (41 C) heat.
In Ohio, severe storms knocked out power to about 1 million homes and businesses on Friday across two-thirds of the state. Governor John Kasich sought and was granted federal emergency assistance.