While the world has various agreements that restrict arms themselves, "there are no real restrictions on weaponisation", he said on Tuesday (early Wednesday AEST) at his first in-person United Nations General Assembly meeting since Russia's invasion.
Zelenskyy took to the world stage at a sensitive point in his country's campaign to maintain international support for its fight.
Nearly 19 months after Moscow launched a full-scale invasion, Ukrainian forces are three months into a counteroffensive that has not gone as fast or as well as initially hoped.
Ukraine and its allies cast the country's cause as a battle for the rule of international law, for the sovereignty of every country with a powerful and potentially expansionist neighbour, and for the stability of global food, fuel and other supplies that have been rocked by the war.
The commodity upheaval has triggered inflation and caused serious hardships for poor countries.
He warned on Tuesday that no nation can be secure if "we allow Ukraine to be carved up", as he tries to rally support for Kyiv's effort to repel a nearly 19-month-old Russian invasion that has no end in sight.
The US president called on world leaders to not let support for Ukraine diminish, arguing that Russia is counting on countries to grow tired of prolonged conflict in Kyiv, which will "allow it to brutalise Ukraine without consequence".
Russia alone is standing in the way of a resolution, Biden argued, saying that Moscow's price for peace was "Ukraine's capitulation, Ukraine's territory and Ukraine's children".
"I ask you this: If we abandon the core principles of the United States to appease an aggressor, can any member state in this body feel confident that they are protected?" Biden said in his address.
"If we allow Ukraine to be carved up, is the independence of any nation secure?
"I'd respectfully suggest the answer is no.
"We have to stand up to this naked aggression today to deter other would be aggressors tomorrow."
During his address, Biden described the partnerships that the US government was fostering around the globe — from Africa to the Indo-Pacific — that he said were creating economic and other advancements, even as he stressed that those relationships were not about "containing any country" — a clear reference to Beijing.
"When it comes to China, let me be clear and consistent," Biden said.
"We seek to responsibly manage the competition between our countries so it does not tip into conflict."
In his 30-minute address, Biden repeatedly emphasised the value of institutions such as the United Nations and international coalitions that has helped the world confront significant challenges such as poverty and disease, as well as echoing his defence of democracy, a common theme of his presidency.
"We will not retreat from the values that make us strong," Biden said.
"We will defend democracy — our best tool to meet the challenges that we face around the world. And we're working to show how democracy can deliver in ways that matter to people's lives."
The annual forum is a chance for Biden to showcase to other world leaders — and the 2024 US electorate — that he's reestablished US leadership on the world stage that he says was diminished under former President Donald Trump.
There were some notable absences as Biden made his case before the General Assembly: British Prime Minister Rishi Sunak, French President Emmanuel Macron, Chinese President Xi Jinping and Putin are all skipping the gathering.
Australian Prime Minister Anthony Albanese remained in Australia campaigning for the Voice referendum Yes vote but foreign Minister Penny Wong travelled to New York.
For Biden, the more important audience for Tuesday's speech could be closer to home as he looks to make the case to voters that he's skilfully handled a complicated foreign policy agenda and that the experience that comes with age has proved to be an asset.
It's an argument that the 80-year-old president is likely to continue to make to try to counter skepticism — even in his own Democratic Party — among voters who are concerned about his age.
"We rallied the world to support Ukraine and united NATO because I was convinced from the beginning that Putin's counting on NATO not being able to stick together," Biden said at a fundraiser on Monday.
"He's still trying. And our allies know once again, the United States can be counted on."
Biden's message of unwavering support for Ukraine will play out as Congress is increasingly divided over providing additional funding for Kyiv.