Ukraine's state-owned energy utility Naftogaz does not agree on prepayment of gas it receives by Russia, the country's Energy Minister Yuriy Prodan said.
The Ukrainian government has confirmed that thousands of Russian soldiers are withdrawing from the Russian territories bordering Ukraine.
Up to twelve people could have died in the city of Donetsk in Ukraine's east since Saturday, according to various reports.
EU states' foreign ministers have given the green light to an arrangement between Russia and the EU under which integration with Ukraine will be postponed for a year.
Ukrainian authorities and pro-Russia rebels on Saturday agreed on a complete ceasefire and a buffer zone a bid to bolster the preliminary truce signed on September 5.
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