The accident occurred in the Oranovo coal mine near the town of Simitli, 110 kilometers (70 miles) south of Sofia. Officials said torrential rains over the past few days may have caused the collapse. The two miners were trapped 300 meters (yards) underground. They were taken to hospital in critical condition but died later of their injuries.
It was the second serious accident this year in the same coal mine. In March, two miners died and another seven were severely injured in an explosion caused by the ignition of a methane gas buildup.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969