Kiev, Ukraine (CNN) -- The U.N. General Assembly on Thursday approved a resolution calling the Crimean referendum to secede from Ukraine invalid.
The vote on the nonbinding resolution was 100-11, with 58 countries abstaining.
It's the latest indication of Russia's isolation within the international community over its actions in Ukraine.
Moscow formally annexed Ukraine's southern Crimea region last week, days after the controversial referendum in which a majority of Crimeans voted to leave Ukraine for Russia.
Adding to tensions, Russia now may have as many as 40,000 troops near its border with Ukraine, two U.S. officials told CNN on Thursday. The officials said that this estimate was largely based on satellite imagery and that a firm number is difficult to assess.
However, a spokesman for Ukraine's Council of National Security and Defense told CNN his government estimates 88,000 Russian troops are at the Ukrainian border.
U.S. officials said they believe the higher estimates may reflect Russian troops on alert farther to the east.
Earlier Thursday, former Ukrainian Prime Minister Yulia Tymoshenko, released from jail last month, said she intends to run for president in May elections.
After more than two years in prison, she was released in February after the ouster of her archrival, President Viktor Yanukovych.
She has already been Prime Minister twice before and ran for President in 2010.
"Yes, I am planning to run," she said at a news conference at her Kiev office.
Tymoshenko said she intended to ask delegates at her Batkivshchyna Party congress on Saturday to nominate her as a presidential candidate.
Ukraine's elections are taking place against a backdrop of poor economic conditions, Moscow's annexation of Crimea and rumblings of discontent in the mainly Russian-speaking eastern regions.
Tymoshenko's announcement came as the International Monetary Fund announced a $14 billion to $18 billion bailout for Ukraine to avoid bankruptcy. The bailout is tied to painful reforms as the country faces an escalating standoff with Russia.
U.S. President Barack Obama on Thursday praised the loan agreement between the IMF and Ukraine, and said the United States will do its part to help, too.
Speaking with Italian Prime Minister Matteo Renzi in Rome, Obama said he is calling on Congress to make sure the United States does its part with an economic assistance package to "support the Ukrainian people as they move forward."
The U.S. Senate on Thursday approved $1 billion in loan guarantees for Ukraine, along with sanctions against Russia for its intervention in Ukraine.
Obama said he hopes that Russia will walk through the "door of diplomacy" but that its annexation of Crimea means the United States and European Union will increase their sanctions.
Earlier this month the House of Representatives approved Ukraine loan guarantees and is now voting on sanctions.
Symbol of 'Orange Revolution'
With her trademark hair braid, Tymoshenko came to international prominence during the 2004 "Orange Revolution" that toppled Yanukovych's first administration.
A rerun of the election handed the presidency to her political ally, Viktor Yushchenko, under whom she was Prime Minister. Amid broad disappointment with that government's performance, Yanukovych was again elected in 2010.
Tymoshenko was imprisoned in 2011 in a corruption case linked to a gas deal she brokered with Russia in 2009. She served two years of a seven-year term, mainly under prison guard in a hospital in Kharkiv.
Many demonstrators carried her picture during mass anti-government protests that began in November and eventually ousted Yanukovych.
Upon her release from prison, Tymoshenko, in a wheelchair, addressed crowds in Kiev's Independence Square, the epicenter of the rallies that began when Yanukovych spurned a deal with the EU in favor of closer ties with Moscow.
Early presidential elections in Ukraine are scheduled for May 25. Former boxer Vitaliy Klitschko and billionaire businessman Petro Poroshenko are also expected to take part in the elections.