A World War II bomb went off early Friday in the eastern Czech city of Ostrava after a man tried to cut it during excavation work, killing him and injuring another.
Police said on Twitter the dead man probably mistook the bomb for an old sewage pipe.
"He used an angle grinder to cut up the metal and the bomb went off," they added.
"We can confirm it was an aerial bomb explosion," police spokeswoman Eva Michalikova told AFP.
Local media said a 49-year-old man died while a 31-year-old man suffered a light head injury.
Police evacuated about 50 people from houses within 300 metres (yards) of the site.
World War II ammunition and bombs are often found in the northeastern Czech Republic through which the Red Army advanced in the spring of 1945.
Last year alone, police evacuated hundreds of people on three occasions because of unexploded aerial bombs.