KIEV, Ukraine — Warning that it was "on the brink of disaster," Ukraine put its military on high alert Sunday and appealed for international help to avoid what it feared was the possibility of a wider invasion by Russia.
Outrage over Russia's military moves mounted in world capitals, with Secretary of State John Kerry calling on President Vladimir Putin to pull back from "an incredible act of aggression." Putin was silent Sunday.
A day after Russia captured the Crimean peninsula without firing a shot, fears grew in the Ukrainian capital and beyond that Russia might seek to expand its control by seizing other parts of eastern Ukraine. Senior Obama administration officials said the United States now believes that Russia has complete operational control of Crimea, a pro-Russian area of the country, and has more than 6,000 troops in the region.
Faced with the Russian threat, Ukraine's new government moved to consolidate its authority, naming new regional governors in the pro-Russia east, enlisting the support of the country's wealthy businessmen, and dismissing the head of the country's navy after he declared allegiance to the pro-Russian government in Crimea.
Ukrainian Prime Minister Arseniy Yatsenyuk said there was no reason for Russia to invade Ukraine and warned that "we are on the brink of disaster."
"We believe that our Western partners and the entire global community will support the territorial integrity and unity of Ukraine," he said in Kiev.
World leaders rushed to try to find a diplomatic solution to the crisis.
NATO held an emergency meeting in Brussels, Britain's foreign minister flew to Kiev to support its new government, and Kerry was to travel to Ukraine on Tuesday. The United States, France and Britain debated the possibility of boycotting the next Group of Eight economic summit, to be held in June in Sochi, the host of Russia's successful Winter Olympics.
On Sunday evening, the White House issued a joint statement on behalf of the Group of Seven saying they are suspending participation in the planning for the forthcoming summit because Russia's advances in the Ukraine violate the "principles and values" on which the G-7 and G-8 (the world's seven leading industrialized nations plus Russia) operate.
In Kiev, Moscow and other cities, thousands of protesters took to the streets to either decry the Russian occupation or celebrate Crimea's return to its former ruler.
"Support us, America!" a group of protesters chanted outside the U.S. Embassy in Kiev. One young girl held up a placard reading: "No Russian aggression!"
"Russia! Russia!" the crowd chanted in Moscow.
Kerry, interviewed on U.S. TV news shows, talked about boycotting the G-8 summit, as well as possible visa bans, asset freezes and trade and investment penalties against Russia.
Asked about a G-8 boycott, Putin's spokesman, Dmitry Peskov said: "It's not a minus for Russia. It will be a minus for the G-8."
Ukraine's new government came to power last week following months of pro-democracy protests against the country's pro-Russian president, Viktor Yanukovych, and his decision to turn Ukraine toward Russia instead of the European Union. Yanukovych fled to Russia after more than 80 people were killed in the protests, but insists he's still president. Russia moved into Crimea amid the crisis.
Ukraine's acting president, Oleksandr Turchynov, put Ukraine's armed forces on alert Sunday, calling up reserves for training. No overt military actions by Ukraine were seen.