MOSCOW -- A day after the Russian leader Vladimir Putin proposed to President Barack Obama that they boost attempts to resolve their standoff over Ukraine, Secretary of State John Kerry scrambled his travel plans to meet with his Russian counterpart in Paris on Sunday, according to a State Department official.
The meeting comes amid fears that Russia plans to seize more Ukrainian territory after its recent rapid annexation of Crimea that led to U.S. and European sanctions.
As the tug-of-war over Ukraine's future continued, Vitali V. Klitschko -- one of the best-known faces of the anti-government protests that helped set off the country's political crisis -- threw his support to a competitor for the presidency in hopes of unifying forces behind a single, pro-Western candidate.
The announcement by Klitschko, a former world champion boxer, that he would put aside his presidential ambitions in favor of the billionaire chocolate magnate Petro Poroshenko reordered the race ahead of elections in May. The move appeared to reflect rising concern of a split in support among candidates who want closer relations with the West, including the former prime minister, Yulia V. Tymoshenko, that could create an opening for a pro-Russia challenger and sow further divisions in a country already riven by months of political upheaval.
"The presidential elections in Ukraine on May 25 should join society and not become another war of everyone against everyone," Klitschko said at a meeting of his party, the United Democratic Alliance for Reform. "This can be achieved only if you do not split the votes between the democratic candidates."
The months of demonstrations, which eventually toppled Viktor Yanukovych, the president at the time, centered on whether Kiev would tilt more toward Moscow or the West and eventually spilled over into the worst strains between Russia and the United States and its allies since the end of the Cold War.
On Saturday, in an apparent bid to defuse those tensions, the Russian foreign minister, Sergey V. Lavrov, said in a television interview that Russia had "no intention" of invading Ukraine, although the United States and NATO have said Russian forces were massed along the Ukrainian border.
Lavrov and Kerry spoke by telephone on Saturday after Obama and Putin had agreed on fresh diplomacy. Kerry then delayed his return to the United States and headed for Paris to meet Lavrov on Sunday.
"We are bringing our approaches closer together," Lavrov said in an interview on Rossia 1 television, according to a transcript on the station's website. "My latest meeting with John Kerry in The Hague and my contacts with Germany, France and some other countries show that the possibility of a joint initiative is taking shape, which could be proposed to our Ukrainian colleagues."
One Obama administration official on Sunday cautioned that it is unlikely that a deal is imminent and noted the difference in tone between the statements issued by the United States and by Russia on what was said in the telephone call between the two presidents. (The White House stressed possible diplomatic movement, while the Kremlin stressed Putin's complaints about "extremists" in Ukraine.) Russia's solution to the impasse over Ukraine emphasizes a federation, allowing for greater autonomy for eastern and southern Ukraine, with their heavy concentration of ethnic Russians. The stress Moscow places on the federation concept is seen partly as an attempt to ensure that Ukraine does not coalesce into a strong pro-European, anti-Russian country right next door.
Lavrov rejected as "absolutely unacceptable" the formula devised by Western officials, whereby Russia and Ukraine would negotiate directly with each other under Western auspices. The Russians reject the current leadership in Kiev as illegitimate. And although he said there were no plans for another takeover, Lavrov also repeated that the West should do more to curb the "lawlessness" in Ukraine; that formulation is often interpreted as a veiled warning that Russia might intervene if the West and its allies do not push the Ukrainian leadership to bring stability.
The move by Klitschko on Saturday could propel Poroshenko to a formidable lead in the election, where his most prominent anticipated contender is Tymoshenko, the country's former prime minister and a familiar if controversial figure in the country's fractious opposition movement. But it might also help Tymoshenko by removing one popular rival.
Klitschko said he would run instead for mayor of Kiev, with a goal of transforming the city into a "truly European capital."
Poroshenko hailed the decision by Klitschko to step aside, saying it would serve the goals of the thousands of people who demonstrated for more than three months in hopes of putting Ukraine on the path to a pro-Western political future.
"It would be a betrayal if we did not unite," Poroshenko said in a speech to the United Democratic Alliance for Reform congress Saturday.
Poroshenko said that it was clear in light of the popular uprising, and the deaths of more than 80 demonstrators in clashes with the police before Yanukovych's ouster, that officials had an obligation to be more responsive to the public.
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On Thursday, Tymoshenko announced that she would run for president as the candidate of the Fatherland party. Tymoshenko, Yanukovych's archrival, spent 21/2 years in prison on charges that her supporters and the West have long criticized as politically motivated. Yanukovych narrowly defeated her in Ukraine's 2010 presidential election.
A spokesman for Tymoshenko, who was attending her own party congress, did not have an immediate response to Klitschko's announcement.
Tymoshenko is by the far the best-known politician in the race. But she faces an uphill climb, given the public's deep mistrust of previous governments in a country with a long history of corruption and mismanagement.
In addition, although she has had extremely harsh words for Russia over the annexation of Crimea, she had a cordial relationship with the Kremlin as prime minister and was regarded as someone with whom Putin could do business -- history that has spurred additional questions about what she might be like as president.
By NEIL MacFARQUHAR and ANDREW ROTH
The New York Times