President Volodymyr Zelensky has said Ukraine "against all odds" is "alive and kicking" as he thanked Americans for their support in a speech to Congress in Washington.
Zelensky received thunderous applause from lawmakers before making his address to a joint session of Congress.
"I hope my words of gratitude resonate in each American's heart," the president began as he said it was a "great honour" to speak in the chamber.
"Against all odds, doom and gloom, Ukraine didn't fall, Ukraine is alive and kicking," he said.
The United States has responded to Zelensky's defiant trip by pledging more money to assist Ukraine pursue a "just peace".
Earlier Joe Biden welcomed Zelensky to the Oval Office, saying the US and Ukraine would continue to project a "united defence" as Russia wages a "brutal assault on Ukraine's right to exist as a nation."
During the address to Congress, Zelensky declared that Ukraine "will never surrender" and warned that the stakes of the conflict were greater than just the fate of his nation - that democracy worldwide is being tested.
"This battle cannot be ignored, hoping that the ocean or something else will provide protection," he said, speaking in English for what he had billed as a "speech to Americans."
He added: "Our two nations are allies in this battle and next year will be a turning point, I know it."
Zelensky, on his first known trip outside his country since Russia invaded in February, has said he wanted to visit earlier and his visit now showed the "situation is under control, because of your support."
The highly sensitive trip was taking place after 10 months of a brutal war that has seen tens of thousands of casualties on both sides and devastation for Ukrainian civilians. Zelensky's visit has been meant to reinvigorate support for his country in the US and around the world, amid concerns that allies are growing weary of the costly war and its disruption to global food and energy supplies.
"Your money is not charity," Zelensky, also told Congress. "It's an investment in the global security and democracy that we handle in the most responsible way."
Just before his arrival, the US announced a $1.8 billion military aid package for Ukraine, including for the first time Patriot surface-to-air missiles, and Congress planned to vote on a spending package that includes about $45 billion in emergency assistance to Ukraine.
Biden said Russia is "trying to use winter as a weapon, but Ukrainian people continue to inspire the world."
Pressed on how Ukraine would try to bring an end to the conflict, Zelensky rejected Biden's framing of a "just peace," saying, "For me as a president, `just peace' is no compromises." He said the war would end once Ukraine's sovereignty, freedom and territorial integrity were restored, as well as the "payback for all the damages inflicted by Russian aggression."
"There can't be any `just peace' in the war that was imposed on us," he added.
Later, in a joint news conference, Biden said Russian President Vladimir Putin has "no intention of stopping this cruel war."
The two leaders appeared to share a warm rapport, laughing at each others' comments and patting each other on the back throughout the visit, though Zelensky made clear he will continue to press Biden and other Western leaders for ever more support.
He said that after the Patriot system was up and running, "we will send another signal to President Biden that we would like to get more Patriots."
"We are in the war," Zelensky added with a smile, as Biden chuckled at the direct request. "I'm sorry. I'm really sorry."
Biden said it is "important for the American people, and for the world, to hear directly from you, Mr President, about Ukraine's fight, and the need to continue to stand together through 2023."
