PRAGUE (AP) — The death toll in a methane explosion that hit a coal mine in northeast Czech Republic increased to 13, a mining company said Friday.

OKD mining company spokesman Ivo Celechovsky said that 11 of the dead were Polish nationals while two were Czechs. Another 10 miners were injured in the explosion Thursday afternoon at the CSA mine near the town of Karvina. Previously, the death toll stood at five.

The Czech public television said three of the injured were still hospitalized in the city of Ostrava, with one of them in critical condition. The explosion occurred about 800 meters (2,600 feet) underground.

Polish Prime Minister Mateusz Morawiecki and Czech counterpart Andrej Babis have offered their condolences to the families of the victims. The two leaders were expected to arrive at the mine on Friday.

"I wish to express words of deepest sympathy to all the close victims of the mining disaster in Karvina," Morawiecki said. "This is a huge tragedy for all Poles and Czechs. On this difficult day, we strongly show our solidarity and sense of national community."

Polish President Andrzej Duda also expressed his condolences on Twitter, saying "O Lord, keep the families of the miners in your care. RIP."