Many in Kiev believe Moscow has its sights on Ukraine’s strategic Crimea peninsula on the Black Sea - once a jewel of Russia’s empire.
Officials both here and in the West worry how far Russia might go to stop Ukraine’s drive to join NATO and to regain control of Crimea.
Analysts say war between the two nations is highly unlikely. While Georgia is a small nation of 4.6 million, Ukraine is roughly the size of France, with a population of 46 million.
Russia also relies on Ukraine for transporting its gas to European consumers, and Russia is Ukraine’s energy supplier and top trading partner.
"There is no way on earth that these two countries will go to war," said Geoffrey Smith, strategist at the Renaissance Capital investment bank in Kiev.
Short of war, however, the Kremlin has many ways of using economic and military might to pressure Ukraine’s Western-backed government.
Russia drew harsh criticism from the United States and Europe last week for recognizing two separatist Georgian territories as independent states following a short but devastating war. Russian troops still control a key Georgian Black Sea port and other locations deep inside the country.
The conflict plunged relations between Moscow and the West to a post-Cold War low and the European Union is considering sanctions against Russia.
French Foreign Minister Bernard Kouchner suggested last week that Russia might next target Ukraine and its neighbor Moldova, a tiny, impoverished ex-Soviet republic which is plagued by its own separatist conflict in the Transdniestria region.
"It is not impossible. I repeat, it’s very dangerous," Kouchner told Europe-1 radio. "There are other objectives that we can assume are objectives for Russia, in particular Crimea, Ukraine and Moldova."
Ukrainian leaders also are alarmed.
"The decision taken by the Russian leadership poses a threat to peace and stability both in our region and in Europe," President Viktor Yushchenko said Wednesday. Only NATO can guarantee Ukraine’s independence, he said.
Vladimir Putin, the powerful Russian prime minister and former president, sought Friday to allay concerns and said that talk of Russia targeting Ukraine "smacks of a provocation."
"Russia has long recognized the borders of today’s Ukraine," Putin told Germany’s ARD television. He added that Crimea is struggling with ethnic tensions, but that it was Ukraine’s internal problem.
Since he came to power four years ago, Yushchenko has made joining NATO his top goal, sought to create a Ukrainian Orthodox church independent of Moscow, and enforced the use of the Ukrainian language at the expense of the Russian - all steps that anger Russia.
Crimea carries an immense emotional resonance for Russians: It was part of the Russian empire for centuries, a beloved tourist destination and home to the proud Russian naval base in the port of Sevastopol.
But in 1954, the Crimea was handed to the Soviet republic of Ukraine by leader Nikita Khrushchev, who had lived and worked there for years. After the 1991 Soviet breakup, it remained part of independent Ukraine.
Back then, Russia was fighting its own separatists and struggling with a collapsing economy - and was too weak to protest.
But by sending troops to Georgia, an economically and politically revived Russia demonstrated a willingness to use military force outside its borders to achieve its aims.
The Kremlin has not officially laid claims to Crimea, but Moscow’s powerful mayor, Yuri Luzhkov, whose views often reflect popular sentiments, has warned that it still not too late for Ukraine to return "what doesn’t belong to it".
Crimea, like Georgia, is a tinderbox of political and ethnic problems. Nearly 1.2 million of its 2 million residents are ethnic Russians, many of whom believe Crimea should be Russian.
Russia has a lease that gives it control of the Sevastopol military base until 2017 and has hinted that it does not want to leave when the lease runs out.
Konstantin Zatulin, a member of the Russian parliament from the Kremlins dominant United Russia Party, has warned that if Kiev is not friendly toward Moscow, it will pay a price.
"This will heat up the situation," Zatulin told the Russian daily Izvestia. "In Ukraine, in the Crimea and in Russia there will be political forces who will be developing the thesis of the need to reconsider borders and the fate of Crimea and Sevastopol."
Several Western leaders rushed to Ukraine’s support.
"We have not forgotten our commitments to you. Nor shall we do so," said British Foreign Secretary David Miliband, who flew to Kiev last week. U.S. Vice President Dick Cheney is expected to visit in September.
