President Volodymyr Zelenskiy says that progress in Ukraine's counteroffensive against Russian forces was "slower than desired" but that Kyiv would not be pressured into speeding it up as its troops advance through dangerous minefields.
"Some people believe this is a Hollywood movie and expect results now. It's not," Britain's BBC quoted him as saying in an interview on Wednesday.
"What's at stake is people's lives."
Ukraine says its long-awaited first counteroffensive for seven months has reclaimed eight villages so far.
But its forces so far have yet to push their way to the main defensive lines that Russia has had months to prepare. Kyiv is believed to have set aside 12 brigades of thousands of troops each for the assault, most of which have yet to join the fight.
Reuters has visited some villages recaptured by Ukrainian forces and confirmed an advance of several kilometres. Moscow says it has been resisting the Ukrainian advances since early June.
The BBC quoted Zelensky as saying the military push was not going easily because 200,000 sq km of Ukrainian territory had been mined by Russian forces.
"Whatever some might want, including attempts to pressure us, with all due respect, we will advance on the battlefield the way we deem best," he added.
After a flurry of early gains, Kyiv has claimed to have captured only one additional village over the past week, the hamlet of Pyatikhatky. Officials said on Wednesday forces in the south were mostly consolidating earlier gains, while troops in the east were holding off Russian attacks.
"They had partial success over the past day, they have consolidated at the boundaries that were reached and they have evened up the front line," Deputy Defence Minister Hanna Maliar said.
Zelenskiy's interview with Britain's public broadcaster was timed to coincide with a conference in London where allies were due to pledge billions of dollars in economic and reconstruction aid.
Washington offered $US1.3 billion ($A1.9 billion). Ukraine's Prime Minister Denys Shmyhal told the conference Kyiv was hoping for more than $US6 billion ($A8.9 billion) from the event.
The West has already given Ukraine tens of billions of dollars worth of military equipment, including hundreds of tanks and armoured vehicles that form the core of the force it is set to unleash in its counteroffensive.
Some of Ukraine's supporters worry that Kyiv will have to show impressive results on the battlefield in coming weeks or risk political support waning in the West.
Both sides have stepped up longer range attacks with missiles and drones in preparation for the fighting at the front.
Russia said on Wednesday it had shot down drones that had reached the region surrounding Moscow. Kyiv never comments on reports of attacks inside Russia.
