KIEV (REUTERS) - Fugitive Ukrainian President Viktor Yanukovych, ousted after bloody street protests in which demonstrators were shot by police snipers, is wanted for mass murder, authorities announced on Monday.

As rival neighbours east and west of the former Soviet republic said a power vacuum in Kiev must not lead to the country breaking apart, acting President Oleksander Turchinov said Ukraine's new leaders wanted relations with Russia on a "new, equal and good-neighbourly footing that recognises and takes into account Ukraine's European choice".

European Union foreign policy chief Catherine Ashton will travel to Ukraine on Monday, where she is expected to discuss measures to shore up the ailing economy, which the finance ministry said required US$35 billion (S$44 billion) in foreign aid over the next two years, with the first tranche needed within two weeks.

Mr Yanukovych, who vanished on Saturday, is still at large.

"An official case for the mass murder of peaceful citizens has been opened," acting interior minister Arsen Avakov wrote on his Facebook profile. "Yanukovych and other people responsible for this have been declared wanted," he said.

Yanukovych had left a private residence in Balaclava, in the Russian-speaking Crimea region, for an unknown destination in a car with one of his aides, Mr Avakov said.

On Independence Square in central Kiev, cradle of the uprising, barricades of old furniture and car tyres remained in place, with smoke rising from camp fires among tents occupied by diehards vowing to stay until elections in May.

The mood among the few hundred on the square was a mixture of fatigue, sorrow for the 82 people killed last week, and a sense of victory after three months of protests. A large video screen by the side of the stage was showing the faces of the dead, one after another, on a loop.

"Now is not the time for celebrating. We are still at war. We will stay here as long as we have to," said Mr Grigoriy Kuznetsov, 53, dressed in black combat fatigues.

Ms Galina Kravchuk, a middle-aged woman from Kiev, was holding a carnation. "We are looking to Europe now. We have hope. We want to join Europe, " she said.

Russia on Sunday recalled its ambassador in Ukraine for consultations on the "deteriorating situation" in Kiev.

A day after Mr Yanukovych fled, parliament named its new speaker, Mr Turchinov, as interim head of state. An ally of the ousted leader's rival, Ms Yulia Tymoshenko, he aims to swear in a government by Tuesday that can run things until a presidential election on May 25.

With battle-hardened, pro-Western protesters in control of Kiev and determined to hold their leaders to account, lawmakers rushed through decisions to cement their power, display their rejection of rampant corruption and bring to account officials who ordered police to fire on Independence Square.

But whoever takes charge as interim prime minister faces a huge challenge to satisfy popular expectations and will find an economy in deep crisis.

Scuffles in Crimea and some eastern cities between supporters of the new order in Kiev and those anxious to stay close to Moscow revived fears of separatism that a week earlier were focused on the west, where Ukrainian nationalists had disowned Mr Yanukovych and proclaimed self-rule.

President Barack Obama's national security adviser Susan Rice was asked on US television about the possibility of Russia sending troops to Ukraine, which President Vladimir Putin had hoped Mr Yanukovych would keep closely allied to Moscow.

"That would be a grave mistake," Ms Rice said on Sunday. "It's not in the interests of Ukraine or of Russia or of Europe or the United States to see a country split. It's in nobody's interest to see violence return and the situation escalate."

Mr Yanukovych's flight left the Russian president's Ukraine policy in tatters, on a day he had hoped eyes would be on the grand finale to the Sochi Olympics. The Kremlin leader spoke on Sunday with German Chancellor Angela Merkel, whose foreign minister had brokered a short-lived truce in Kiev on Friday.

They agreed Ukraine's "territorial integrity" must be maintained, Dr Merkel's spokesman said.

British Foreign Secretary William Hague was asked if Russia might "send in the tanks" to defend its interests among ethnic Russians in the east and on the Crimea peninsula, where Moscow bases its Black Sea Fleet. "It would really not be in the interests of Russia to do any such thing," he told the BBC.

Earlier this month, a Kremlin aide had warned that Moscow could intervene.

It is unlikely the United States and its allies in NATO would risk an outright military confrontation with Russia, but such echoes of the Cold War underline the high stakes in Ukraine, whose 46 million people and sprawling territory are caught in a geopolitical tug of war.

EU officials offered financial aid to a new government and to revive a trade deal that Mr Yanukovych spurned under Russian pressure in November, sparking the protests that drove him from office.

In addition to any economic assistance the EU might offer, the United States has also promised help. Budgets are tight on both sides of the Atlantic, and international creditors may be wary of Mr Yanukovych's opponents, whose previous spell in government was no economic success.

But a desire to avoid instability and back what looks to Western voters like a democratic movement menaced by Russian diktat may loosen purse strings, at least to tide Ukraine over until elections.

US Treasury Secretary Jack Lew encouraged Ukraine to begin discussions with the International Monetary Fund on an assistance package as soon as possible once a transitional government is in place in Kiev.

Mr Lew spoke with Mr Arseny Yatsenyuk, a member of Ukraine's interim leadership, while returning to Washington from the G20 meeting in Sydney, where there was broad support for an IMF-based package, according to a Treasury official In Russia, where Mr Putin had wanted Ukraine as a key part in a union of ex-Soviet states, the finance minister said the next tranche of a US$15 billion loan package agreed to in December would not be paid, at least before a new government is formed.

Russian Foreign Minister Sergei Lavrov, according to his office, told US Secretary of State John Kerry the opposition had "seized power" by force by ignoring an EU-brokered truce that would have left Mr Yanukovych in office for the time being.

But even lawmakers from Mr Yanukovych's own party voted for his removal on Saturday and blamed him and his entourage for the crisis. Business "oligarchs" also distanced themselves from a man long seen as their representative in the presidency.

In a mark of passions dividing Ukrainians along a historic fault line between Russian and Ukrainian cultures, local television in Ketch, in eastern Crimea, showed a crowd hauling down the blue-and-yellow Ukrainian flag in front of the town hall and hoisting the white, blue and red Russian tricolour.

In a hectic round of voting in parliament, lawmakers rushed in some crowd-pleasing measures against the old administration, conscious that those still occupying Independence Square - or the Maidan - remained deeply suspicious of the political class.

They stripped Mr Yanukovych of his abandoned country home near Kiev, complete with ostrich farm and hot tubs, its brash opulence fuelling demands that he be held to account for stealing taxpayer billions.

Mr Turchinov said a government should be in place by Tuesday.