* Yanukovich wanted for mass murder, minister says
* Country needs $35 billion in next two years
* Parliament appoints new speaker acting president, election May 25
* Acting president says European integration a top priority
* Yanukovich last seen in Crimea
Fugitive Ukrainian President Viktor Yanukovich, ousted after bloody street protests in which demonstrators were shot by police snipers, is wanted on an arrest warrant 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 was travelling to Ukraine to discuss measures to shore up the ailing economy, which the finance ministry said needs $35 billion in foreign aid over the next two years.
Russian-backed Yanukovich, 63, who fled Kiev by helicopter on Friday, is still at large after heading first to his eastern power base, where he was prevented from flying out of the country, and then diverting south to the Crimea, acting interior minister Arsen Avakov said.
"An official case for the mass murder of peaceful citizens has been opened," Avakov wrote on his Facebook profile. "Yanukovich and other people responsible for this have been declared wanted."
Yanukovich had left a private residence in Balaclava, in the Russian-speaking Crimea, for an unknown destination by car with one of his aides and a handful of security guards, Avakov said.
It was an ignominious political end for Yanukovich who has been publicly deserted by some of his closest erstwhile allies, stripped of his luxury residence outside Kiev and had to witness the return of his arch-rival Yulia Tymoshenko.
Russia recalled its ambassador from Kiev for consultations on Sunday, accusing the opposition of having torn up a transition agreement with the president it supported.
In a sign of nervousness over how Moscow may react, Oleh Tyahnybok, a far-right nationalist who was one of three opposition leaders who negotiated with Yanukovich on Friday, said the Defence Ministry should check out reports that Russian troops might gather on Ukraine's border.
He gave no details and did not suggest such troop movements had actually taken place. Interfax news agency later quoted Ukrainian border guards as saying there was no sign of any Russian troop movements near the border.
Tyahnybok said a boat was due to arrive in the Crimean port of Sevastopol with 200 Russian commandos. Russia's Black Sea fleet is based in Sevastopol and its forces come and go freely. It was not clear whether this was a long-scheduled arrival.
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 Grigoriy Kuznetsov, 53, dressed in black combat fatigues.
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 Yanukovich fled, parliament named its new speaker, Turchinov, as interim head of state. An ally of the ousted leader's rival, 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 former leaders to account, lawmakers rushed through decisions to cement their power, show their rejection of rampant corruption and bring to justice officials who ordered police to fire on Independence Square.
Whoever takes charge faces a huge challenge to satisfy popular expectations and will find an economy in deep crisis and which faces state debt payments of around $6 billion in the remainder of this year.
The Finance Ministry said it needed $35 billion in foreign assistance over the next two years and appealed for urgent aid. It called for a donors' conference involving representatives of the European Union, the United States and the International Monetary Fund.
The hryvnia currency fell by 3.8 percent on Monday after the weekend drama before recovering slightly. The cost of insuring Ukraine's debt fell on hopes that the country would now receive aid and avoid default, while sovereign dollar bonds recorded gains on expectations that a new government would focus on the economy.
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. A week ago those concerns were focused on the west, where Ukrainian nationalists had disowned Yanukovich and proclaimed self-rule.
President Barack Obama's national security adviser, Susan Rice, was asked on U.S. television about the possibility of Russia sending troops to Ukraine, which President Vladimir Putin had hoped Yanukovich would keep closely allied to Moscow.
"That would be a grave mistake," 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."
Yanukovich's flight left Putin'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, Merkel's spokesman said.
British Foreign Secretary William Hague was asked if Russia might "send in the tanks" to defend its interests. "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 Yanukovich 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 through the International Monetary Fund, which has demanded painful economic reforms as a condition.
In Russia, where Putin had wanted Ukraine as a key part in a union of ex-Soviet states, the finance minister said the next tranche of a $15 billion loan package agreed to in December would not be paid, at least before a new government is formed.