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 said 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 said 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.

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.  

IMF offers Ukraine lifeline with tough terms

The International Monetary Fund pledged up to US$18 billion in loans yesterday to prop up Ukraine's teetering economy, and the prime minister warned that everyone will feel some pain from the necessary reforms ahead.

Meanwhile, former Ukrainian prime minister Yulia Tymoshenko announced that she will run for president in the vote set for May 25. Tymoshenko, who was released from jail last month following the overthrow of President Viktor Yanukovych, returns as one of the most polarizing figures in Ukraine's political scene.

In a lengthy, passionate address to parliament in Kiev, Prime Minister Arseniy Yatsenyuk warned that Ukraine was "on the brink of economic and financial bankruptcy" and laid out the fixes needed to put it back on track.

"The time has come to tell the truth, to do difficult and unpopular things," Yatsenyuk said. "The country is short 289 billion hryvnia (US$25.8 billion), which is practically equivalent to the entire state budget for this year."

The IMF loan, which is expected to range between US$14 billion and US$18 billion, hinges on structural reforms that Ukraine has pledged to undertake.

Ukraine's new government finds itself caught between the demands of international creditors and a restive population that has endured decades of economic stagnation and mismanagement. The reforms demanded by the IMF - which included raising taxes, freezing the minimum wage and hiking energy prices - will hit households hard and are likely to strain the interim government's tenuous hold on power.

Other donors, including the European Union and Japan, have also pledged further aid, conditional on the conclusion of an IMF bailout. The total amount of assistance will be about US$27 billion over the next two years.

Tymoshenko will make a second attempt to win the presidency. She narrowly lost to Yanukovych in 2010 and spent two years in jail on corruption charges.

"I will be the candidate of Ukrainian unity," Tymoshenko said yesterday. "The west and center of Ukraine has always voted for me, but I was born in the east."

Ukraine is politically divided, with western regions favoring closer ties to Europe and the east looking toward Russia. But the dire state of its economy is an unavoidable issue: Ukraine says it needs US$35 billion over the next two years to avoid default.