Ukrainian President Viktor Yushchenko and is due in Russia in an effort to improve ties between the two countries.
His discussions with President Vladimir Putin come amid a dispute over gas debts that could see Moscow cutting its gas supply to Ukraine.
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Gazprom, which supplies 25% of Europe's gas, said the dispute will not affect supplies to the rest of Europe.
But as most of the company's gas supply to western Europe passes through Ukraine, concerns remain that the row could escalate into a repeat of two years ago.
In January 2006, gas shipments to Europe were disrupted after Russia halted fuel supplies to Ukraine for several days amid a fierce argument over price hikes.
US concern
Although Gazprom claims the dispute is purely commercial, fears have been raised that Moscow might be exploiting its energy resources to exert political pressure on its neighbours.
US State Department spokesman Sean McCormack said Washington was monitoring the situation.
"We've made it quite clear in the past our views as to the use of commercial levers to try to achieve some political purpose in the end," he said.
On Monday, Gazprom and the Ukrainian state energy companies failed to resolve the gas debt dispute during several hours of talks.
Gazprom extended its deadline for cutting a quarter of gas supplies to Ukraine until 1500GMT on Tuesday, to allow Mr Yushchenko to discuss the matter with Mr Putin.
Meanwhile, Ukraine's pro-Western Prime Minister Yulia Tymoshenko appealed for calm and suggested that Gazprom's threats were empty.
She said that Russian First Deputy Prime Minister Sergei Ivanov had informed her "that a cut-off will not take place".
(BBC)
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