Ukraine's interim leadership pledged to put the country back on course for European integration now Moscow-backed Viktor Yanukovich had been ousted from the presidency, while the United States warned Russia against sending in its forces.
As rival neighbors 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 late on Sunday that Ukraine's new leaders wanted relations with Russia on a "new, equal and good-neighborly footing that recognizes 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.
Russia said late on Sunday it had recalled to Moscow its ambassador in Ukraine for consultations on the "deteriorating situation" in Kiev.
A day after Yanukovich fled to the Russian-speaking east following dozens of deaths during street protests aimed at toppling him, parliament named new speaker Turchinov as interim head of state. An ally of the ousted leader's long-jailed rival Yulia Tymoshenko, he aims to swear in a government by Tuesday that can provide authority until a presidential election on May 25.
With battle-hardened, pro-Western protesters in control of central 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 book 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 Russian-speaking 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 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. "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."
Yanukovich's flight into hiding 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 in a statement.
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 Yanukovich spurned under Russian pressure in November, sparking the protests that drove him from office after 82 deaths last week, many from police sniper fire.
In addition to any economic assistance the EU might offer, the U.S. has also promised help. Budgets are tight on both sides of the Atlantic, and international creditors may be wary of Yanukovich'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.
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 in December would not be paid, at least before a new government is formed.
Russian Foreign Minister Sergei Lavrov, according to his office, told U.S. Secretary of State John Kerry the opposition had "seized power" by force by ignoring an EU-brokered truce that would have left Yanukovich in office for the time being.
But even lawmakers from Yanukovich'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 faultline between Russian and Ukrainian cultures, local television in Kerch, 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 tricolor.
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 - remain deeply suspicious of the political class.
They stripped Yanukovich 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.
Turchinov said a government should be in place by Tuesday.
His ally, Tymoshenko, defeated by Yanukovich in a 2010 presidential election and later jailed for corruption, ruled herself out as interim premier. Freed from a prison hospital on Saturday after more than two years in jail, she may want time to recover and build support before running for the presidency.
As prime minister following the largely peaceful Orange Revolution of 2004-05, which overturned a first presidential victory by Yanukovich, Tymoshenko disappointed many in Ukraine who had hoped for an end to the corruption and failed economic policies that marked the aftermath of Soviet communism.
"In these days the most important thing is to form a functioning government," said Vitaly Klitschko, a former world boxing champion and also a possible presidential contender.
On Independence Square, men were still wandering around with clubs and wearing home-made body armor, helmets and in some cases ski masks and camouflage fatigues.
"We'll stay here to the very end," said one, Bohdan Zakharchenko, 23, from Cherkasy, south of Kiev. "We will be here till there's a new president."