Vladimir Putin will keep driving the war forward wider and deeper if he is not stopped, Ukraine's President Zelensky has warned.
Speaking at the UN's General Assembly in New York, Zelensky said more countries would be met with Russian aggression unless allies displayed a united front and ramped up support.
He said all nations were threatened by a global arms race, as military technology advances, adding that weapons decide who survives and calling for global rules on AI.
His comments come after US President Donald Trump shifted his position on the Russia-Ukraine war, saying for the first time that Ukraine could win back all of its land.
Zelensky criticised international institutions, suggesting they are too weak to offer Ukraine safety guarantees, adding - in apparent reference to Nato - that being part of a long-standing military alliance doesn't automatically mean you are safe.
We are now living through the most destructive arms race in human history, he said.
He argued that stopping Russia now was cheaper than wondering who will be the first to create a simple drone carrying a nuclear warhead.
Zelensky called for international rules around AI and its role in weaponry, and said the development of autonomous drones and unmanned planes represented a far greater risk than traditional warfare.
The Ukrainian leader also warned that Europe cannot afford to lose Moldova - which lies between Ukraine and EU-member Romania - to Russian influence. He said the West had missed a chance to save Georgia and Belarus from Putin's orbit.
On Thursday the pro-EU president of Moldova, Maia Sandu, accused the Kremlin of pouring hundreds of millions of euros into Moldova in an attempt to instigate violence and spread fear.
Last week, Estonia and Poland requested a consultation with other Nato members after Russia violated its airspace in separate incidents.
Earlier on Tuesday, following his speech to the UN, Trump said Nato nations should shoot down Russian planes breaching their airspace, following the recent incursions by Russian fighter jets and drones.
Zelensky praised Donald Trump and said he had a good meeting with the US president.
On Tuesday, he told reporters he understood the US was willing to give Ukraine security guarantees after the war is finished. Pressed on what this would look like, he said he did not have specific details but broached the possibility of more weapons, air defences and drones.
The US president also described Russia as a paper tiger that had been fighting aimlessly in Ukraine. Kremlin spokesman Dimitry Peskov responded: Russia is in no way a tiger. It's more associated with a bear. And there is no such thing as a paper bear.
A recent meeting between US Secretary of State Marco Rubio and his Russian counterpart Sergei Lavrov marked the highest-level US encounter with Russia since Trump invited Putin to Alaska last month.
Rubio reiterated Trump's call for the killing to stop and the need for Moscow to take meaningful steps toward a durable resolution of the Russia-Ukraine war.
