At least 12 miners have been killed in a methane gas explosion at a coal mine in southern Poland. An official said the blast struck the Wujek-Slask mine in Ruda Slaska-Kochlowice and at least 15 miners were seriously injured. Thirty eight miners were working more than a kilometer underground at the time of the accident. Medical staffs have warned that death toll may rise. The explosion is thought to have been caused by the ignition of a pocket of methane gas. This is the worst mining accident in Poland since a methane gas explosion killed 23 miners at the Halemba mine in Silesia three years ago.