MOSCOW — For weeks, the world waited with bated breath as tens of thousands of Russian troops massed on the border with Ukraine amid the worst East-West crisis since the end of the Cold War.
Now, with senior U.S. officials confirming that Moscow has begun at least a partial pullback of its forces, the immediate danger of a Russian invasion of Ukraine appears to be fading. Russian President Vladimir Putin has vowed to work with his newly elected Ukrainian counterpart, Petro Poroshenko, and Kremlin-controlled media have toned down their aggressive rhetoric.
"Russia's stance has changed dramatically," said Fyodor Lukyanov, a Moscow-based political analyst and editor-in-chief of Russia in Global Affairs magazine.
One telling sign of the Kremlin's changing attitudes, Mr. Lukyanov said, is its reaction to Kiev's expanding "anti-terrorist" operation in eastern Ukraine. About 50 pro-Moscow separatists have lost their lives in the conflict-hit region in recent days, including during an airborne assault by government forces on the international airport in Donetsk, the biggest city under rebel control.
Despite repeated pleas for military assistance from the leaders of self-proclaimed "people's republics" in the Russian-speaking region, Kremlin spokesman Dmitry Peskov would commit Friday only to humanitarian aid for the insurgents. Mr. Peskov would not be drawn on the issue of more substantial assistance for the insurgents, who held referendums in May on independence from Ukraine. Mr. Putin said publicly that those referendums should not go forward.
"At the end of April, when Kiev began its operation in the east of Ukraine, Russia's reaction was very sharp. Troops were moved closer to the border and military maneuvers were carried out. Now, although there is a real war going on in the region, with the use of aviation and so on, Russia's reaction is much more muted," Mr. Lukyanov said.
Although analysts are quick to note that there was never any solid evidence that Russia was planning a full-scale invasion of Ukraine, they have few doubts that the very option of direct military intervention is off the Kremlin's table, at least for now.
So what has changed?
"I would say that the prospect of broader sanctions against Russia — so-called sectorial sanctions — was certainly a factor [in Putin's change in tone]," said Maria Lipman, an analyst with the Moscow-based Carnegie Center.
The West in April imposed sanctions against banks and energy companies controlled by some of Mr. Putin's closest allies over the Kremlin's annexation of Ukraine's Black Sea peninsula of Crimea. In mid-May, Secretary of State John F. Kerry warned that Washington and its European allies would move ahead with heavier sanctions if Russia disrupted Ukraine's May 25 presidential polls.
"The West sent a very clear, totally unambiguous message," Ms. Lipman said.
Ms. Lipman also suggests that the Kremlin may have decided not to risk ruining the success of this spring's bloodless annexation of Crimea with a much riskier and costlier invasion of eastern Ukraine, where popular support for joining Russia is far lower.
The annexation of Crimea, which was gifted from Russia to Ukraine in 1954 by Soviet leader Nikita Khrushchev, was wildly popular with Russians across the political spectrum. Mr. Putin's approval ratings have since shot up to a record 83 percent, according to a poll released last week by the independent Moscow-based Levada-Center. In another survey, by the state-run VTsIOM pollster, almost half of respondents said they believe Russia is on the verge on regaining its Soviet-era status as a superpower.
"The return of Crimea was seen as a reason to be proud for many people in Russia," Ms. Lipman said. "It's likely that the change of rhetoric and policy is designed so as not to tarnish that good feeling."
However, Sergei Markov, a Kremlin-connected analyst who has advised the Russian government on Crimea, said Mr. Putin could find himself under pressure to send troops to Ukraine if civilian casualties mount as part of the ongoing military operation against separatist forces.
"Putin could also remove obstacles to Russian volunteers going to the region, as well as transfer weaponry, including anti-aircraft equipment, that would even things out there," he said.
Ukrainian authorities frequently have accused Russia of supplying separatists in eastern Ukraine. A number of insurgent fighters also told Western media last week that they were from Chechnya, the volatile republic in Russia's North Caucasus region. There is no conclusive proof, however, that these fighters are acting on the orders of the Russian government.
Mr. Lukyanov, the editor and analyst, suggested that Mr. Putin's shifting mood is connected to the realization that war with neighboring Ukraine would have "extremely unpredictable consequences," at home and in the international arena.
"Everyone realizes that any military operation in Ukraine, a country which shares a common history, culture and religion with Russia, would be a catastrophe," he said. "Russia will only take this step if it considers it absolutely necessary.
"Besides, as things stand, Kiev has very little chance of victory in east Ukraine," he said. "Despite the use of heavy weaponry there, and the rising death toll, it has so far failed to bring the region under control. So why would Russia even need to invade?"