According to Ukrinform, Andriy Yermak, the head of Ukraine's presidential office, said this in an interview with Japan's public broadcaster NHK.
"In this war, we will never make concessions in terms of our independence, territorial integrity, and sovereignty," he said.
Yermak noted that the next few months will be pivotal for Ukrainian troops on the battlefield.
In his opinion, an extended conflict could favor the Russian forces.
Yermak said that if the fighting in this war lasts until winter, it will be more difficult for Ukraine to regain its territory.
"We are focusing our discussions on taking all possible measures to break the deadlock before that time comes around," he said.
Yermak added that Ukrainian troops have been intensifying counterattacks in the south, noting that their goal is to win back 100 percent of the territory seized by Russia.
He also called on the U.S. and Western allies to impose further sanctions against Russia. He said leaders in Moscow continue to use energy exports as leverage to lift the sanctions.