Ukraine's acting president has accused "Kremlin agents" of fomenting deadly violence in eastern cities, in one of the most direct and highest-level criticisms aimed by Kiev at President Vladimir Putin.

From his speaker's chair in parliament on Saturday, interim head of state Oleksander Turchinov referred to three deaths in two incidents this week in Donetsk and Kharkiv.

On the eve of a breakaway vote in the southern Crimea region, he told opposition lawmakers: "You know as well as we do who is organising mass protests in eastern Ukraine - it is Kremlin agents who are organising and funding them, who are causing people to be murdered."

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Turchinov has warned of a risk of a Russian invasion of the east following Moscow's occupation of the Crimea peninsula.

Ukrainian officials have called on people in the mainly Russian-speaking cities of the industrial east not to rise to provocation that Russia might use to justify sending in troops.

On Friday US Secretary of State John Kerry failed to either avert Sunday's ballot in Crimea or win Russian Foreign Minister Sergey Lavrov's assurance that Moscow may delay annexing the Black Sea region that Ukraine only received as a "gift" from Soviet leader Nikita Khrushchev in 1954.

East-West showdown

The rugged peninsula of two million mostly Russian speakers is widely expected to vote to split from Ukraine and join Russia after its lawmakers declared independence from Kiev earlier this month, amid the biggest East-West showdown since the Cold War.

The referendum comes in direct response to three months of deadly protests that on February 22 toppled the pro-Kremlin president and brought to power a new nationalist European-leaning team in Kiev, infuriating Moscow that views Ukraine as its strategic sphere of influence and wants to retain influence over its former Soviet satellite.

Kiev has denounced the Crimean vote as illegal but is also warily watching as similar separatist sentiments are being fanned by Moscow supporters in other regions in eastern Ukraine, which has deep cultural and trade ties to Russia.

Yet Moscow - whose troops took effective control of Crimea in the days after the President Viktor Yanokovich's fall last month - strongly backs the referendum despite a new round of painful sanctions against top Russian officials that Washington and EU nations are expected to unveil on Monday.

Source: Agencies