BOGOTA (AFP) - The death toll from an explosion at a coal mine in northern Colombia, believed to have been caused by an accumulation of methane gas, has risen to seven, authorities said Friday. Colombia's mining regulator Ingeominas had last put the death toll from Wednesday's incident at the El Diamante mine in the town of Socha in Boyaca department at three. Emergency personnel subsequently retrieved the bodies of four more miners who had been trapped under the rubble, Ingeominas said. More than 40 people have been killed in mining accidents in Colombia so far this year, most of them in cave-ins. Last year, 173 people were killed in 84 reported accidents, many due to insufficient security measures. President Juan Manuel Santos has sought to boost the mining sector as a pillar of Colombia's economic growth.