Biden spoke today after meeting with Ukrainian officials in their capital, Kyiv.
The vice-president also announced the United States will provide an additional $50 million to help Ukraine's beleaguered government with political and economic reforms.
The money includes $11 million to help conduct the May 25 presidential election, including voter education, administration and oversight.
It also will help fund expert teams from U.S. government agencies to help Ukraine to reduce its reliance on energy supplies from Russia. Other technical advisers will help fight corruption.
The White House has also announced $8 million in nonlethal military assistance for the Ukrainian armed forces, including bomb-disposal equipment, communications gear and vehicles.