Russian Foreign Minister Sergei Lavrov said on Wednesday that Ukraine is on the brink of civil war, making it difficult to hold free and fair elections later this month.
Lavrov added that pro-Moscow separatists should be included in Western-sponsored roundtable unity talks due to begin Wednesday.
"When Ukrainians kill Ukrainians I believe this is as close to a civil war as you can get," Lavrov said in an interview with Bloomberg television.
Lavrov added that "in east and south of Ukraine there is a war, a real war, with heavy weaponry used.
"And if this is conducive to free and fair elections then I don`t recognise what free and fair is."
Ukraine is due to hold crunch presidential elections on May 25.
But the transitional government in power since the ouster of Ukraine`s pro-Russian leader Viktor Yanukovych in February is leading an offensive against separatists who have overrun several towns and proclaimed sovereignty in two regions after referendums.
Lavrov insisted the rebels should be included in the talks on Wednesday, being held under a roadmap drafted by the pan-European security body the OSCE after the failure of a deal hammered out in Geneva last month.
"We believe that for this national dialogue to succeed it is absolutely necessary to ensure equal participation of all regions of Ukraine," he said.
This included not only separatists in the east and south "but also the regions of the west where we also have some issues related to self-determination of minorities."
But the Russian minister insisted that Moscow had "no intention" of sending in troops to eastern Ukraine after the referendums there, as it did when it absorbed the disputed region of Crimea.
"We respect the outcome of this referendum and we don`t have any intention to send any troops anywhere," Lavrov said.
He said however that he had "strong suspicions" that Western mercenaries were operating in Ukraine.
"We have very strong suspicions that this might be true," he said.
As the EBRD development bank warned that Russia`s economy would face stagnation this year while Ukraine will slump into recession, Lavrov played down the threat of further US and EU sanctions over the crisis.
"I don`t think that economic sanctions are being considered seriously from the point of view of the responsibility of the West in the international economic system," Lavrov said.