Twenty-five miners were killed Monday after a coal mine explosion deep in the rugged hills of West Virginia, marking the worst U.S. mine disaster since 1984 and raising questions about safety precautions at one of the nation’s largest coal producers.

The search for survivors at the Upper Big Branch mine was called off early Tuesday morning, although four miners remained unaccounted for, according to Jeff Gillenwater, spokesman for Massey Energy Co., the mine owner.

Distraught families and others in the tight-knit Appalachian mining community wept and hugged nearby as rescue teams penetrated the deep shafts and dark tunnels, and as the death toll steadily rose through the long night.

The explosion about 3 p.m. Monday had disabled communication lines, including wireless systems, inside the vast underground complex, officials said.

Officials had raised hopes during the day that many of the missing miners might have used emergency escape routes to reach specially reinforced, airtight chambers that are stocked with food, water and air about a mile and a half below ground. If so, the sites could sustain them for several days.

Officials said they didn’t yet know the cause of the accident. But federal mine safety and health officials have repeatedly cited Massey, one of the nation’s largest coal producers, and the mine’s operator for potentially dangerous conditions, including venting of combustible methane gas.

Violations in recent weeks include cracking and collapsing of mine walls on Feb. 21; ventilation problems on March 17, March 23 and March 30; drill dust on March 25; and inadequate air quality on March 23; according to U.S. records.

In the last year, federal inspectors have fined the company more than $382,000 for repeated serious violations involving its ventilation plan and equipment at the mine, the Associated Press reported.

At least nine mine rescue teams, state and federal officials, and distraught families had converged on the Appalachian mining town of Montcoal, about 30 miles south of Charleston, the state capital.

Elizabeth Pellegrin, a spokeswoman for the Charleston Area Medical Center, said one miner was flown in by helicopter at 6 p.m.

The miner was in intensive care, she said, and doctors were preparing for other patients.

“We’re hoping for more,” Pellegrin said.

The mine employs about 200 people, but not all would have been underground on the afternoon shift.

President Obama offered his condolences to the families of the miners, according to the White House.

The president spoke by phone Monday night with Gov. Joe Manchin III and offered federal assistance in the rescue.

“For those families who are still waiting for news on their missing loved ones, I want them to know that we are doing everything possible in cooperation with federal officials and the company to get our miners out as quickly and safely as possible,” Manchin said in a statement released by his office.

“We are all working diligently together and I ask that everyone pray for the miners, their families and our rescue teams,” he added.

Earlier in the evening, Don Blankenship, Massey Energy’s chairman and chief executive, confirmed seven deaths “with a heavy heart.”

He said the company would not release the names until next-of-kin were notified.

“Our top priority is the safety of our miners and the well-being of their families,” Blankenship said in a statement.

“We are working diligently on rescue efforts and continue to partner with all of the appropriate agencies.

“Our prayers go out to the families of the miners. We want to assure the families of all the miners we are taking every action possible to locate and rescue those still missing,” he said.

Kevin Stricklin, administrator for coal mine safety and health in the U.S. Department of Labor, told the Associated Press that seven men apparently were killed while riding out of the mine on a vehicle, and that two other men aboard the vehicle were injured.

Stricklin said officials don’t believe the roof collapsed.

Jeff Gray, director of emergency services with the Central West Virginia Chapter of the American Red Cross, said officials were scrambling to get medical and mental health services to the site.

“It’s a very rural area,” he said.

About seven miles from the mine, the First Baptist Church in Whitesville prepared sandwiches, hot dogs and soda for grieving families Monday evening, said Dennis Dye, a church deacon.

“We’re prepared for them to come and we want them to come,” he said.

The mine, operated by Massey subsidiary Performance Coal Co., produced 1.2 million tons of coal in 2009, according to the Mine Safety and Health Administration.

Massey Energy says on its website that it has an above-average safety record, with three fatalities at the Upper Big Branch mine in the last 12 years.

In 1998, a miner was killed when a support beam failed and dropped bags of cement mix onto him, according to the federal Mine Safety & Health Administration. Federal investigators blamed poor welding and construction.

Another miner died there in 2001 when part of the mine’s roof collapsed, and an electrician was accidentally electrocuted while repairing a shuttle car in 2003.

Massey Energy is a publicly traded company based in Richmond, Va. It has 2.2 billion tons of coal reserves in southern West Virginia, eastern Kentucky, southwest Virginia and Tennessee, according to the company’s website.

bob.drogin@latimes.com

nicole.santacruz@ latimes.com