Protesters hold a poster during a protest against Russia's plans to increase gas prices for Ukraine, at the Russian Embassy in Kiev

Ukraine's prime minister is rejecting a planned price hike by Russia's state-run natural gas company, Gazprom, as an unacceptable move aimed at putting direct economic pressure on Ukraine.

Yuriy Yekhanurov told officials in Kiev his country will take all necessary legal steps if the dispute is not resolved. His comments came as Ukraine's energy minister, Ivan Plachkov, left for Moscow for talks on a settlement.

Gazprom intends to more than quadruple the price it charges Ukraine to bring its prices in line with the world market. Kiev supports an increase but wants a gradual one to avoid damaging its economy.

Gazprom is threatening to cut supplies on January first if no deal is reached. Ukraine says it has sent its proposals and will seek international arbitration if there is no agreement.