Russian Prime Minister Vladimir Putin has warned the European Union that its supply of gas may be affected if Ukraine does not clear its arrears. Moscow says the country has not paid its gas bill for the month of October.

Russia is the world's biggest natural gas producer and the European Union depends on Russian gas pumped via Ukraine for around a fifth of its total gas consumption. In January, a week-long row between Russia and Ukraine led to gas supplies to more than a dozen European countries being turned off. This caused problems for hundreds of thousands of households.

Sweden, currently chair of the EU, says it is keeping the situation under close observation. Mr Putin has suggested that the EU lend Ukraine money should it become necessary.

Photos of Vladimir Putin and natural gas tanks by ANP