Any peace deal with Russia would depend on Russian forces pulling back to their pre-invasion positions, Ukraine's president says.
Speaking to a London think tank, Volodymyr Zelensky said that was the minimum that his country could accept.
He said he was the leader of "Ukraine, not a mini-Ukraine". But he did not mention Crimea, annexed by Russia in 2014.
Russia is currently battling to take full control of the city of Mariupol.
There are still Ukrainian forces along with some civilians in the south-eastern city's vast Azovstal steelworks, which has been subjected to a furious Russian onslaught.
Finally taking Mariupol would be Russia's biggest achievement in two months of war and would give Russia's President Vladimir Putin something to celebrate on 9 May, which is Victory Day in Russia - the day the country marks the Soviet victory over the Nazis in World War Two.
However speaking from Kyiv to the Chatham House think tank in London, Mr Zelensky said there could be no question of Russia holding on to territory it has conquered since it invaded Ukraine.
"To stop the war between Russia and Ukraine the step should be regaining the situation as of 23 February," he said in response to a question from the BBC, referring to the day before the war began.
"I was elected by the people of Ukraine as president of Ukraine, not as president of a mini Ukraine of some kind. This is a very important point," he added.
The reference to the situation as of 23 February suggests Ukraine may not insist on retaking Crimea before making peace with Russia. The peninsula was annexed by Russia eight years ago.
Mr Zelensky called for the resumption of diplomatic dialogue between Russia and Ukraine: "Despite the fact that they destroyed all our bridges, I think not all the bridges are yet destroyed, figuratively speaking," he said.
Russia, for its part, has described that process as being in a "state of stagnation".