US President Joe Biden has also agreed to give Ukraine anti-personnel land mines, a US defence official told the BBC.
But Zelensky said Ukraine was going through a “very difficult period” on the battlefield.
The Russian military is accelerating its gains along the front line, according to data from the Institute for the Study of War (ISW).
Its analysis found Russian forces seized six times more territory in 2024 than it did in the previous year.
Based on confirmed social media footage and reports of troop movements, the ISW said Moscow’s forces seized around 2,700 sq km of Ukrainian territory so far this year, compared with just 465 sq km in the whole of 2023.
Ukraine’s surprise incursion into Russia’s Kursk region is faltering as Russian troops have pushed Kyiv’s offensive backwards.
Zelensky also had harsh words for German Chancellor Olaf Scholz for speaking to Putin on the phone last week.
He told Fox News it was a “Pandora’s box” because Putin’s isolation would increase the pressure on him.
