U.S. President Barack Obama says ensuring Ukraine is financially stable is an important way to influence Russian decision-making.
Mr. Obama spoke in Rome Thursday after the International Monetary Fund pledged $18 billion in loans to Ukraine, and the U.S. Congress approved another $1 billion.
Following talks with Italian leaders, Mr. Obama said the United States and Europe are going to have to put a lot of resources and effort into Ukraine.
The IMF loans come with a requirement for Ukraine to carry out tough economic reforms.
Meanwhile, the head of Ukraine's national security council, Andriy Parubiy, says Russia has close to 100,000 troops along Ukraine's borders in the north, south, and east.
He said during a webcast to a Washington audience that Russian forces are in full readiness to strike.
A Pentagon spokesman said Thursday that Russia continues to reinforce the area but that Russia's intent is unclear.
Russian Defense Minister Sergei Shoigu said last week the solders are involved in "springtime exercises." He assured U.S. Defense Secretary Chuck Hagel that they would not cross the border.
Western experts believe the number of Russian forces near eastern and southern Ukraine is closer to 30,000.
Also Thursday, the United Nations General Assembly adopted a resolution that refuses to recognize Russia's annexation of Ukraine's Crimean peninsula.
One-hundred countries voted for the non-binding resolution. Eleven opposed it and 58 abstained.
Russian ambassador Vitaly Churkin said before the vote that the resolution was "confrontational in nature" and that Crimeans have the right to self-determination.
In Ukraine Thursday, former Prime Minister Yulia Tymoshenko announced she is a candidate for the May 25 presidential election.
Ms. Tymoshekno narrowly lost the 2010 election to ousted President Viktor Yanukovych. She spent more than two years in jail over a natural gas deal with Russia when she was prime minister. Her supporters say the charges were political revenge by Mr. Yanukovych.