Kiev - Ukrainian President Petro Poroshenko warned Thursday that nationalist protesters blocking a railway to the coal-rich Russian-backed separatist east could cause power outages across the country and job losses as a result.Ultranationalists have blocked a railway line since the start of the year between the coal-producing east and the rest of Ukraine to protest against Kiev trading with the rebels.Kiev has declared a state of emergency in the energy sector over the blockade and Poroshenko called it a "destabilising factor" for the war-scarred and cash-strapped former Soviet state.Poroshenko warned in a speech that due to the coal delivery stoppage several big cities and parts of the capital "may be left without heating".He said the protest could cost Ukraine "300 000 jobs" because factories will grind to a halt without the required power."And the state will lose $2 billion in hard currency earnings," he added.The Ukrainian leader said this would force the local currency lose value and make life more expensive for ordinary people.The activists blocking shipments believe Ukraine should not be trading with its foe and that the insurgents are using the freight trains to shuttle weapons and fighters to flashpoints in the war.Kiev buys a specific type of coal produced only in the eastern self-proclaimed Donetsk People's Republic to fuel the power plants that provide the country's electricity and centralised heating.UtranationalistsThe trade has gone on even as Kiev and the separatists are locked in a 34-month conflict that has claimed more than 10 000 lives.Prime Minister Volodymyr Groysman said on Wednesday that the railway protest was a "crime" that could leave hospitals and homes without power.Energy Minister Igor Nasalyk warned that Ukraine was preparing for a month of possible rolling blackouts and urged consumers to sharply curtail their electricity use.The country has been beset by problems ranging from a war it blames on Russia to a complete lack of control of its vital industrial east where the rebels have set up their own fiefdoms.Poroshenko is walking on thin ice because direct condemnation of the protests risks further angering the ultranationalists.The protesters on Thursday vowed to continue."The blockade will go on!" they said in a statement."All the threats by the corrupt authorities only confirm that we are on the right path and give us strength and inspiration," they said.