In an overnight address, Ukraine’s leader also repeated his call for Nato to impose a no-fly zone, warning it was “only a matter of time before Russian missiles fall on your territory”.
As Russia’s invasion of Ukrain entered a 19th day, the UK Ministry of Defence said Russian naval forces had established a distant blockade of Ukraine’s Black Sea coast, isolating the country from international maritime trade.
In eastern Ukraine, Russian troops were trying to surround Ukrainian forces as they advance from the port of Mariupol in the south and the second city Kharkiv in the north, it added.
In his latest video address released shortly after midnight, Mr Zelensky said: “We are going through the worst ordeal in our history. In our lives.
“We protect the most precious thing we have. We must hold on. We must fight. And we will win. I know that. I believe in that.”
Referring to efforts to arrange a meeting between him and Russian president Vladimir Putin, he said this is “a hard path, but this path is needed”.
Meanwhile, reports emerged on Monday that Russia has asked China for military equipment to use in its invasion of Ukraine.
News of the request comes ahead of a Monday meeting in Rome between top aides for the US and Chinese governments.
In advance of the talks, White House national security adviser Jake Sullivan bluntly warned China to avoid helping Russia evade punishment from global sanctions that have hammered the Russian economy. “We will not allow that to go forward,” he said.
A US official, speaking on condition of anonymity to discuss sensitive matters, said that in recent days, Russia had requested support from China, including military equipment, to press forward in its ongoing war with Ukraine.
The official did not provide details on the scope of the request. The request was first reported by the Financial Times and The Washington Post.
The Biden administration is also accusing China of spreading Russian disinformation that could be a pretext for Mr Putin’s forces to attack Ukraine with chemical or biological weapons.
Besieged Ukrainians were holding onto hope that renewed diplomatic talks with Russia, which according to Russian state news agency Tass were set to resume today, might open the way for more civilians to evacuate, a day after Moscow escalated its offensive by shelling areas perilously close to the Polish border.
Russian missiles pounded a military base in western Ukraine on Sunday, killing 35 people in an attack on a facility that served as a crucial hub for cooperation between Ukraine and the Nato countries supporting its defence.
It raised the possibility that the alliance could be drawn into the fight. The attack was also heavy with symbolism in a conflict that has revived old Cold War rivalries and threatened to rewrite the current global security order.
Mr Zelensky called it a “black day” and again urged Nato leaders to establish a no-fly zone over the country, a plea that the West has said could escalate the war to a nuclear confrontation.
“If you do not close our sky, it is only a matter of time before Russian missiles fall on your territory. Nato territory. On the homes of citizens of Nato countries,” Mr Zelensky said, urging Russian President Vladimir Putin to meet with him directly – a request that has gone unanswered by the Kremlin.