Zelensky visited the Pentagon on Tuesday hours after the last US troops left Afghanistan as America's longest-ever war ended with the nearly 20-year-old US-backed government crumbling to the Taliban.
Russian officials have pointed to Afghanistan as a lesson for Ukraine, which has relied on the West in a seven-year war against Moscow-linked separatists, but Biden has insisted that he withdrew to end a costly distraction from a larger US challenge of facing an assertive China and Russia.
Defence secretary Lloyd Austin told Zelensky that the United States was committed to demanding that Russia "stop perpetuating the conflict" in eastern Ukraine and leave Crimea, the peninsula Russia seized from Ukraine in 2014.
"We will continue to stand with you in the face of this Russian aggression," Austin said.
He highlighted a new $60 million package for Ukraine that includes Javelin anti-armour systems. He said the United States has committed $2.5 billion for Ukraine's defence since 2014, when Russia intervened as Ukraine turned increasingly Westward.
The assistance took centre stage in US politics in 2019 when then-president Donald Trump held up military aid as he pressured Zelensky, a comedian turned politician, to dig up dirt on Biden.
Seeing immediate threats
Western European nations have led opposition to Ukraine entering NATO, fearing such a move would provoke Russia.
Zelensky, speaking late Tuesday, said that he was looking more at immediate needs for Ukraine, including its forces on the Black Sea, as more than 13,000 people have died in the conflict.
"We have no time to think about strategy. We have to provide for as much protection as we can to actually prevent a build-up" by Russia, Zelensky said.
"Ukraine needs a modern fleet and for this we need partners," he said. "I would like to discuss this with President Biden."
Russia earlier this year amassed an estimated 100,000 troops on Ukraine's border and in Crimea, prompting fears of an invasion at the start of Biden's term.
Russian forces withdrew in April. But much of the equipment remained and Zelensky voiced concern over a "dangerous" September as Russia carries out military exercises with Belarus, whose authoritarian government has been firmly in president Vladimir Putin's orbit.
Zelensky said Ukraine, still reliant on aging Soviet equipment, wanted to be a greater production partner of the United States and to cooperate more closely on cyber security and preventing disinformation.
"We're not asking for any gifts," Zelensky said. "We need opportunities for our specialists."
He also pledged to ramp up efforts against corruption, a long-running concern for Biden -- who has repeatedly cited graft as a reason for dropping support for the former Afghan government.
Alyona Getmanchuk, director of the New Europe Center in Kiev, wrote in a blog for the Washington-based Atlantic Council that Ukraine was far less dependent on Western support than Afghanistan's former government.
"Even so, the nature of the American withdrawal from Afghanistan has set off alarm bells throughout Ukraine and served as a wake-up call for anyone who still believes that continued Western support can be relied upon indefinitely," Getmanchuk wrote.