Fuel oil spilt in a Russian rail crash has spread to the River Volga and is threatening to pollute the Moscow water supply.
The train was derailed on Wednesday night, and almost 30 of its oil wagons tumbled down a hill towards the River Vazuza - a tributary of the Volga. The crash took place in the Tver region about 200 kilometres from Moscow.
It was not clear how long the oil would take to reach Moscow, but any water supply problems would be a major embarrassment for city authorities after a power cut last month paralysed Russia's political and financial capital.
Television footage showed viscous black oil trickling out of the capsized wagons and running in a heavy slick down to the river. Teams of workers were struggling to prevent more oil reaching the river, and bulldozers were pulling wagons back up the hill.
The emergencies services had deployed two boats on the river to try and break up the oil spill and halt its advance, news agencies reported.
Much of Russia's oil - the country's main export product - is sent by rail as companies strive to avoid bottlenecks in pipelines, which are pumping at capacity.