While Russia "has not been able to achieve its planned results yet", Russian soldiers have outnumbered Ukraine's 8-1, a number that Kyiv cannot match, the president added.
The crucial supply and transport hub in Pokrovsk serves as a lifeline for delivering supplies and reinforcements to the eastern front, and capturing it would bring Moscow closer to taking full control of the Donetsk region.
'Difficult situation'
Zelenskyy has described the situation in Pokrovsk as being "difficult", adding that the town is witnessing widespread fierce fighting after "sabotage groups" entered the region.
The president said that satellite imagery shows that over 200 Russian soldiers are currently inside Pokrovsk. An apparent capture of the city would put towns of the heavily fortified "fortress belt" -- Kramatorsk, Slovyansk, Kostyantynivka and Druzhkivka -- at risk of Moscow invasion.
According to Capt Hryhoriy Shapoval, Russian forces had amassed significant troops and equipment near Pokrovsk, using armoured vehicles to provide cover for their advancing infantry.
"So it's hard to stop them," he said.
Zelenskyy's request to Trump
Meanwhile, Zelenskyy on Tuesday urged US President Donald Trump to pressure Chinese leader Xi Jinping to cut his support for Russia when the two leaders meet later this week.
Trump said he would certainly discuss the Russian invasion of Ukraine when he meets Xi on Thursday in South Korea.
"If President Trump manages to hold talks, make decisions, and reach an understanding with China to reduce imports of Russian energy, I think it will help all of us," Zelensky said at a press conference in Kyiv.
Trump has sought to leverage his personal chemistry with Russian leader Vladimir Putin to end the Ukrainian conflict, but has so far failed to make progress.
With inputs from agencies
