Zelensky also thanked Congress for its "big, huge support."
Ukrainian President Volodmyr Zelensky won pledges of unstinting support and air defense weapons from President Joe Biden on Thursday, but he warned that Russia could still defeat Kyiv if Republican lawmakers cut US military aid.
Wearing his trademark olive green military-style shirt, Zelensky huddled with members of Congress before stopping at the Pentagon and the White House, where Biden greeted him with an honor guard.
"We greatly appreciate the assistance provided by the United States to combat Russian terror, really terror," Zelensky told Biden in the Oval Ofice.
Sitting with Biden beneath portraits of former presidents George Washington and Abraham Lincoln and reading prepared remarks from cards, Zelensky also thanked Congress for its "big, huge support."
Biden hailed the "enormous bravery" of the Ukrainian people as they fight back Russia's invasion, adding that "the American people are determined to see to it that we do all we can to ensure the world stands with you."
"We're supporting a just and lasting peace, one that respects Ukraine's sovereignty and territorial integrity," he said.
But on his second wartime visit to Washington, Zelensky faced a far trickier political landscape than when he arrived to a hero's welcome in December 2022.
While the White House announced it would give him a "significant air defense capability," there was no deal to provide the long-range missiles that Zelensky covets.
And in Congress, Republican and Democratic leaders are locked in a bitter spending battle that could spark a US government shutdown, with a $24 billion aid package for Ukraine at risk.
- 'Lose the war' -
The hard-right faction dominating the Republican Party is increasingly adamant that the aid spigot should be turned off, with Congress having already approved $100 billion in aid to date, including $43 billion in weaponry.
The Ukrainian leader arrived right after another wave of Russian missile strikes. The attacks -- hitting cities across the country -- killed at least three people in Kherson and wounded many in other areas.
Democratic Senate leader Chuck Schumer, a major supporter of Biden's pro-Ukraine policies, said Zelensky had told him "if we don't get the aid, we will lose the war."
As part of his bid to win over Washington, Zelensky went to the Pentagon where he laid a wreath at a memorial for victims of the September 11, 2001 attacks.
White House National Security Advisor Jake Sullivan said he was confident that there would be "strong bipartisan support to continue funding Ukraine" despite the deep US political divide.
But in a blow to Zelensky, he said Biden had rejected for now a request for longer-range ATACMS missiles that can strike up to 300 kilometers (190 miles) away.
On Capitol Hill, Zelensky got a notably discreet welcome from the Republican Speaker of the House of Representatives, Kevin McCarthy, who is having trouble keeping a lid on internal party squabbling over US spending in Ukraine.
Some Republicans say the money could be better spent on US border security, while there are also concerns about the pace of Kyiv's counteroffensive and that corruption in Ukraine means the money will go to waste.
- 'Enough is enough' -
The doubts are being fuelled by messaging from former president and likely 2024 candidate Donald Trump, who has opposed more funding and frequently expressed admiration for Russia's Vladimir Putin.
It's a trend that has also reached parts of the generally more pro-Ukraine Republicans in the Senate, where Senator Roger Marshall said Congress should not be "sending another blank check to Zelensky" and six senators issued a joint letter declaring "enough is enough."
Earlier this week, Zelensky attended the UN General Assembly meeting in New York where he urged the world to stand firm with Ukraine against Russia's "genocide."
His warning came a day before Poland said it would no longer arm Ukraine in a mounting row over grain exports.
But on Thursday, the Polish prime minister said he had been "misinterpreted."
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)