Updated at 10:30 a.m. ET

Ukrainian President Petro Poroshenko addressed a joint meeting of Congress today, thanking lawmakers for their support of Kiev in its fight against Russian-backed separatists.

Freedom, Poroshenko said, is "at the core of Ukrainian existence.

"We have an unbreakable will to live free," he said, saying his nation was "at the center of the most heroic story of the last decade."

Calling Russia's annexation of Crimea a "most cynical act of treachery," Poroshenko thanked lawmakers for standing by his government.

"More of you were with us over the last winter. I thank you for this solidarity," he said to loud applause.

Poroshenko is in the United States to lobby the White House and Congress for increased aid in his country's fight against the insurgency in its eastern provinces.

However, The Washington Post notes: "Amid concerns about Ukraine's commitment to anti-corruption efforts and Western caution about escalating a military conflict with Russia, it remained far from clear that Ukraine's leader would leave Washington with a substantial new pledge of support."

Poroshenko also plans to meet with President Obama, Vice President Joe Biden, Secretary of State John Kerry and House Speaker John Boehner.

The Associated Press writes:

"White House officials made clear that Poroshenko's visit — his first to the U.S. since being elected this summer — was aimed in part at sending a message to Russia about the West's backing for the embattled former Soviet republic." 'The picture of President Poroshenko sitting in the Oval Office will be worth at least a thousand words — both in English and Russian,' White House spokesman Josh Earnest said."

Last week, Boehner said of the Ukrainian leader's plan to visit: "Having President Poroshenko address Congress is another signal of our steadfast commitment to the aspirations of his people."

His visit follows a similar stop in the Canadian capital on Wednesday, where the Ukrainian president was met with cheers and standing ovations in a speech before Parliament.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.