Six Ukrainian soldiers have been killed and eight hurt in an ambush by separatists near Krematorsk, Kiev's Defence Ministry says.

Authorities say the troops were attacked outside the town in the east of the country by at least 30 insurgents using grenade launchers and automatic weapons.

Pro-Russia insurgents have been seizing government buildings and controlling towns and cities across eastern Ukraine for the last month. It comes after two eastern regions, Donetsk and Luhansk, declared independence on Monday.

German Foreign Minister Frank-Walter Steinmeier, speaking earlier at Kiev's main airport, said Germany supported Ukraine's efforts to arrange a dialogue between the central government and its opponents in the breakaway regions.

He said he hope for the quick release of journalists being held hostage by pro-Russia insurgents and that the occupied buildings would be handed back soon.

Mr. Steinmeier also stressed the importance of holding Ukraine's presidential vote as planned on May 25th.

The Ukrainian government and the West have accused Russia of instigating the mutiny in the east to derail Ukraine's presidential vote and possibly grab more land.

Mr. Steinmeier's trip is part of the road map for settling the crisis, as outlined by the Organisation for Security and Cooperation in Europe (OSCE), a trans-Atlantic security group.

Russia called for a swift implementation of the OSCE plan, saying its demand to end violence means that the central government in Kiev should stop its military operation to recapture buildings in the east.

Moscow also says the scheme should compel Ukraine to lift its blockade of cities and towns, pull its forces from eastern regions and release all political prisoners.

Russia's Foreign Ministry said in a statement "We are demanding (they) stop intimidating civilians by using force or threatening to use it".

It added that it expects separatists in Ukraine's Donetsk and Luhansk regions to respond in kind if Kiev does all that.

"(The road map) creates conditions for launching a broad national dialogue involving all political forces and regions of Ukraine, aimed at reconciliation and a comprehensive constitutional reform intended to stop the nation from sliding further to catastrophe" the Ministry said.

Russia also urged the United States and the European Union to persuade Kiev to prioritise talks over giving more powers to Ukraine's regions ahead of the Presidential vote.

The separatists held a referendum on Sunday and claimed around 90% of those who voted in Donetsk and Luhansk backed sovereignty. The two regions declared independence on Monday and those in Donetsk asked to join Russia.

Ukraine's acting president called the vote a sham and Western governments said it violated international law.