Ukrainian President Victor Yanukovych declared Sunday a national day of mourning, two days after 37 miners died in two accidents. The Emergencies Ministry said an explosion 3,000 feet underground at the Sukhodilska-Vostochnaya mine in the east of the country killed 26 people and injured two Friday, CNN said. On the same day, a building collapse at the Bazhanov mine in the southeast killed 11 miners and injured four, but more than 500 managed to escape. Both incidents were unexplained and under investigation Sunday. Regional authorities in Luhansk said preliminary findings on the Sukhodilska explosion will be released Monday, the Ukrainian News Agency reported. An air-methane reaction is suspected. \"The coal mine will not resume operation until the investigation into the reasons for the explosion is done,\" Energy Minister Yurii Boiko said.