Ukraine's interim leaders have pushed a plan to allow the regions a greater say over their affairs.

However, the exclusion of separatists from round table talks today has cast doubt over whether the move could defuse the crisis.

The talks brought together politicians and civil groups in an effort to quell a pro-Russian rebellion in the industrialised Donbass region of eastern Ukraine.

The rebellion has triggered fears of a break-up of the former Soviet republic.

Today's talks came at a tense moment for Kiev; a day after seven soldiers were killed in an ambush near the city of Kramatorsk.

It was the deadliest attack on security forces since they were sent to tackle the uprising in the east in April.

Voters in the eastern regions of Donetsk and Luhansk backed self-rule in two referendums held on Sunday, despite protestations from Kiev.

Kiev sees Russia's hand behind the rebellion and denounced the votes as illegal.

After the voting, rebel leaders in Donetsk and Luhansk called for their regions to become part of Russia although this call has not been taken up by Moscow.

When the round table talks opened in the parliament building in Kiev, the country's main leaders sharply attacked Russia.

Acting president Oleksander Turchinov accused Moscow of launching "systematic action to destabilise eastern and southern regions of Ukraine" to produce an "explosive situation".

In comments angled at the separatist rebels who were excluded from the talks, Prime Minister Arseny Yatseniuk said: "We will conduct a dialogue with all those who do not shoot and do not kill citizens."

But Mr Yatseniuk went on to press a decentralisation plan ceding greater powers to the regions, which the Kiev authorities hope will address disaffection in eastern Ukraine and help undercut the influence of rebels seeking to break altogether with Kiev and join the Russian Federation.

Such a scenario is seen by Kiev as pointing a way to resolving the crisis.

"Using mechanisms for changing the constitution, we should be able to de-centralise power and confer additional powers on regional authorities ... create a real balance (between central and regional authorities)," he said.

Under the plan regions could hold back a portion of taxes for direct use in improving infrastructure and conditions for local businesses.

But the plan's architects are keen that they do not allow discussion of "federalisation" - an idea pushed by Russia and the separatists, which they fear would lead to too-great autonomy and weaken the grip of the central government.

Russian Foreign Minister Sergei Lavrov earlier said that Ukraine is on the brink of civil war, making it difficult to hold free and fair elections later this month.

The speaker of Russia's lower house of parliament said that the president to be elected by Ukraine on 25 May will not be fully legitimate.

Speaking in an interview with Bloomberg, Mr Lavrov said that "when Ukrainians kill Ukrainians I believe this is as close to a civil war as you can get,"

Mr 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."