The attack came hours after President Volodymyr Zelenskiy announced that a second round of US-brokered trilateral talks between Ukraine and Russia would take place next week.
DTEK said in a statement that Russian forces had carried out a "massive terrorist attack" on a company mine in the region and that all the dead and wounded were its employees returning from a shift.
"Today, the enemy carried out a cynical and targeted attack on energy sector workers in the Dnipropetrovsk region," energy minister Denys Shmyhal wrote on the Telegram app.
DTEK and Shmyhal had earlier put the death toll at 15.
Police said the attack took place in the city of Terenivka.
Footage posted by the State Emergencies Service showed a charred bus with shattered windows that had veered off the road.
Earlier on Sunday, regional officials said at least nine had been wounded in Russian strikes on a maternity hospital and a residential building in the southeastern city of Zaporizhzhia.
Sunday's strikes also follow remarks by Zelenskiy earlier in the day that Russia - which said it had agreed to stop attacking Ukrainian energy infrastructure until February 1 - was still targeting logistics in Ukraine.
Zelenskiy said on Sunday that three-way peace talks between Russia, Ukraine and the United States are to take place on Wednesday and Thursday in Abu Dhabi.
Direct negotiations between Ukraine and Russia had been expected to take place on Sunday but it remained initially unclear whether that meeting had been held, with Zelenskiy only saying that his team delivered a report setting out the new dates for the talks in the United Arab Emirates.
Direct negotiations between Russia and Ukraine resumed in Abu Dhabi a week ago after a long hiatus.
They were held behind closed doors and mediated by the United States through its chief negotiator Steve Witkoff.
with DPA
