Ukraine is marking the 25th anniversary of the world's worst nuclear accident at the Chernobyl power plant. It was on 26th of April 1986, that number four reactor at Chernobyl, which was then in the Soviet Union, exploded. The accident forced the evacuation of hundreds of thousands of people from their homes in Ukraine, western Russia and Belarus. There is still a 30 kilometer exclusion zone around the plant. An explosion at one of the plant's reactors sent a plume of radiation across Europe and killed at least 30 people in its immediate aftermath. A number of others died later from radiation-related illnesses. The anniversary comes amid renewed global protest over nuclear power and as Japan struggles to contain radiation leaks at its crippled Fukushima plant. The Russian President Dmitry Medvedev is visiting Chernobyl today.