The death toll from Monday's blast at a U.S. coal mine in West Virginia climbed to 29 after four missing miners were found dead on Friday, local media reported.

The incident at the Upper Big Branch Mine in West Virginia became the worst coal mine disaster in the United States in 40 years.

Local media quoted officials as saying that the search efforts will now shift to recovering all 22 bodies still trapped inside the mine.

Mine deaths are relatively not common in the United States. Last year, the number of U.S. miners killed on the job was 34, 18 of them died in coal mines. Notable accidents in recent years include West Virginia's Sago Mine methane explosion, which killed 12 miners in 2006. Six died in Utah's Crandall Canyon mine cave-in in 2007.

An explosion at a coal mine in southern West Virginia killed 25 miners and left four others missing on April 5, 2010. The accident is the worst mine disaster in the country since a mine fire in Utah killed 27 people in 1984. [Photo: CRI]