Several official military reports have also mentioned small groups of Russian soldiers advancing into Pokrovsk itself.
Russia’s targeting of Ukraine with a new medium-range missile, thought to have implications for all of Europe, is likely to play a major role during discussions.
Mr Zelensky is expected to meet with Prime Minister Donald Tusk around midday.
The UN Refugee Agency warned on Friday that aid was slowing down.
At least eight schools and 10 healthcare facilities, including a maternity hospital, were reportedly damaged in the past week.
“They are also delivering hygiene supplies and other basic items to people in Mykolaiv and Odesa who have been evacuated and sought shelter in those two towns.
Emergency forces have suspended the search for missing people after a Russian missile hit a high-rise residential building in the Ukrainian city of Dnipro.
In sub-zero temperatures, there was little hope of finding any more survivors.
“Winter is coming, and all we want to do is provide insulin to the hospitals, provide blankets, provide mattresses…it’s not complicated,” she said.
“The secretary-general strongly urges all parties to enact an urgent and immediate humanitarian ceasefire.”
