Ukrainian President Petro Poroshenko has asked a joint session of the U.S. Congress for military aid and to confer a special security status upon Ukraine.
In an emotional speech before U.S. legislators, Poroshenko said that his army needed more military equipment, both "lethal and nonlethal."
He said that "blankets [and] night-vision goggles are also important. But one cannot win a war with blankets...and cannot keep the peace with blankets."
Poroshenko mentioned that just since the start of a cease-fire on September 5, Ukraine has lost 17 soldiers.
The Ukrainian president warned of a threat to "global security everywhere" posed by the Russian aggression against his country.
He described Ukraine's conflict with Russia as the world's worst since the U.S.-Soviet Cuban missile crisis in 1962 and urged the United States not to let "Ukraine stand alone in the face of this aggression."
Poroshenko also pleaded with Washington to give Ukraine "special," non-NATO security status to help beef up its defenses against aggression from Russia.
Poroshenko also said that Russia's annexation of Crimea was one of "the most cynical acts of treachery in modern history."
He added that there is "no way, at no price, and under no condition" that Kyiv will put up with the occupation.
The Ukrainian leader also called for the creation of a special fund "to support U.S. companies' investment in Ukraine and help reform our economy and justice system."
Poroshenko said all assistance received by Ukraine from the West will be used "by noncorrupt establishments and the new generation of officials will guarantee that the funding will be used effectively."
In a gesture of support for Poroshenko, the United States pledged $53 million in fresh aid to Ukraine on September 18, including antimortar radar equipment.
Senior U.S. administration officials said the new assistance would include $46 million to bolster Ukraine's security in its conflict with Russian-backed separatists in eastern Ukraine and $7 million in humanitarian aid.
Later, U.S. President Barack Obama met with Poroshenko at the White House.
Poroshenko waves to well-wishers gathered outside the White House as he arrives to meet with U.S. President Barack Obama.
Speaking in the Oval Office after their talks, Obama condemned what he called "Russian aggression, first in Crimea and most recently in portions of eastern Ukraine."
Obama praised Poroshenko for his leadership, saying it has "been critical at a very important time in Ukraine's history."
Obama said the United States would continue to help Ukraine find a diplomatic solution to the crisis the country faces.
Poroshenko thanked Obama for what he said was the "enormous" support the United States has shown Ukraine.
Poroshenko said he and Obama discussed the question of energy and that a U.S. "team" would be in Ukraine next week to review Ukraine's energy situation and needs with winter coming soon.
Meanwhile, a bill authorizing military aid -- including lethal aid -- to Ukraine and putting more sanctions on Russia unanimously passed the U.S. Senate Foreign Relations Committee on September 18.
The Ukraine Freedom Support Act of 2014, authored by Senators Robert Menendez (Democrat-New Jersey) and Bob Corker (Republican-Tennessee), passed by an 18-0 vote.
When and if the bill will come up for a vote in the U.S. Senate is uncertain, as it passed on the last day before the chamber adjourns until November.
The bill goes further than the Obama administration's newly announced aid package on September 18, which authorizes $46 million in nonlethal military aid.
The Menendez-Corker bill authorizes $350 million in military aid, including some forms of lethal aid.
With additional reporting by Reuters, AP, AFP, Interfax, and RFE/RL's Luke Johnson in Washington