(Adds details, comments from Russia, Georgia and others, paragraphs 12-16, 20-21 and 23)
By Louis Charbonneau and Mirjam Donath
UNITED NATIONS, March 27 (Reuters) - The U.N. General Assembly on Thursday passed a non-binding resolution declaring invalid Crimea's Moscow-backed referendum earlier this month on seceding from Ukraine, in a vote that Western nations said highlighted Russia's isolation.
There were 100 votes in favor, 11 against and 58 abstentions in the 193-nation assembly. Two dozen countries did not participate in the vote, either because they did not show up or because they have not paid their dues, U.N. diplomats said.
Western diplomats said the number of yes votes was higher than expected despite what they called Moscow's aggressive lobbying efforts against the resolution.
Before the vote, one senior Western diplomat had described a result with 80-90 yes votes as successful for Ukraine. Other Western diplomats agreed, saying the result showed how few active supporters Moscow has around the world.
The General Assembly resolution echoes a text Moscow vetoed earlier this month in the Security Council. The approved declaration dismisses Crimea's vote as "having no validity, (and) cannot form the basis for any alteration of the status of the Autonomous Republic of Crimea or of the City of Sevastopol."
The resolution, which does not mention Russia by name, says the General Assembly "calls upon all States, international organizations and specialized agencies not to recognize any alteration of the status" of Crimea and Sevastopol.
Although the resolution is non-binding, Western diplomats said it sends a strong political message about Russia's lack of broad support on the Crimean issue. They said the fact that Russia lobbied so hard to persuade U.N. member states not to vote for it was proof that Moscow took it seriously.
Ukrainian Foreign Minister Andriy Deshchytsia, who introduced the text to the assembly, said after the vote that an "overwhelming majority of nations in the world supported this resolution."
"The purpose of this document is to reinforce core United Nations principles at a moment when they are experiencing a major challenge," he said before the vote.
"This text is also about respect of territorial integrity and non use of force to settle disputes," he added. "It sends an essential message that the international community will not allow what has happened in Crimea to set a precedent for further challenges to our rules based international framework."
Speaking before the vote, Russian U.N. Ambassador Vitaly Churkin urged countries to support what he said was Crimea's right of self-determination and to respect the Crimeans' choice to place themselves under the authority of Moscow.
"Russia could not refuse the Crimeans to support their right to self-determination in fulfilling their long-standing aspiration," he said. "Historical justice has been vindicated."
Churkin described the voting result as "a moral victory for the Russian diplomacy."
"The fact that almost half of the members of the United Nations refused to support this resolution, I think, is very encouraging," he said.
Several Western diplomats, however, said Churkin led an aggressive lobbying campaign against the resolution, adding that many states which sympathize with Ukraine abstained or chose not to be present for fear of angering Russia.
Israel, Iran, Serbia and several former Soviet republics in Central Asia like Tajikistan and Kyrgyzstan were among those that did not take part in the vote.
Ukraine's former Russian-backed president, Viktor Yanukovich, was ousted last month after a crackdown on demonstrations in Kiev that left dozens dead. That prompted Moscow to seize the Black Sea peninsula.
U.S. Ambassador Samantha Power said all countries supported the idea of self-determination but that Russia had used its military to forcibly annex Crimea.
"Coercion cannot be the means by which a self determines," she said. "The chaos that would ensue is not a world that any of us can afford. It is a dangerous world."
Power added that the resolution showed "that borders are not mere suggestions."
Kaha Imnadze, the ambassador of Georgia, said Moscow was repeating what it had done in his own country's 2008 war with Russia over the Georgian breakaway enclave of South Ossetia.
"What happened in Ukraine reminds us of what we saw in Georgia in 2008, when Russia seized Georgia's Abkhazia and Tskhinvali regions," he said. "Six years after the war, 20 percent of my country remains under illegal Russian occupation."
Only 10 other countries stood with Russia in voting against the resolution. The group of 11 states, which the senior Western diplomat described as the "dirty dozen", included critics of Western nations like Belarus, Bolivia, Cuba, North Korea, Nicaragua, Sudan, Syria, Venezuela and Zimbabwe.
Both Nicaragua and Bolivia railed against what they described as Western attempts at "regime change", which they said was meant to undermine democratically elected governments.
China, which since 2011 joined Russia in vetoing three Security Council resolutions that condemned Syria and threatened it with sanctions, abstained, as it did in the Security Council vote on Ukraine earlier this month. (Editing by Chizu Nomiyama and Tom Brown)