CITLUK, Serbia—An accident Friday in a coal mine in central Serbia killed eight miners and wounded 18 others, authorities said, adding that the workers apparently suffocated from too much methane gas. The accident in the Soko coal mine, located 200 kilometers (125 miles) southeast of Belgrade, the capital, occurred shortly after 4 a.m. Officials said an investigation was underway to determine exactly what happened. “Inspectors, police and all relevant authorities are at the scene, doing what is necessary to determine the cause of this tragedy,” said the Mining and Energy Minister Zorana Mihajlovic. The state RTS television and other local media initially reported that part of the pit collapsed, releasing the methane gas inside and trapping the miners. But MIhajlovic, who visited the site Friday, denied reports of an explosion. “There was no explosion or anything, but the rise in methane was such that they suffocated,” said Mihajlovic, expressing condolences …