Heavy fighting was underway Sunday in the northern parts of the frontline hotspot Bakhmut, while Ukraine's defence minister said the reluctance of Kyiv's Western allies to send jets would cost it "more lives."
Despite the flow of Western weapons to Ukraine, Russia has claimed gains in recent days around war-ravaged Bakhmut in the eastern region of Donetsk.
The head of the Russian mercenary group Wagner said that fighting raged on in northern parts of Bakhmut.
"In the northern quarters of Artemovsk, fierce battles are going on for every street, every house, every stairwell," Yevgeny Prigozhin said in a statement, referring to Bakhmut by its previous name.
"The Ukrainian armed forces are fighting to the last," he said.
Russian forces have been trying to seize control of Bakhmut in the eastern region of Donetsk for months in what has become the longest and bloodiest battle since Russia invaded Ukraine last February.
"I am sure that we will win this war," Ukraine's Defence Minister Oleksiy Reznikov told a news conference in Kyiv, but he said that without the delivery of Western jets, "it will cost us more lives".
He also pledged that new long-range weapons Kyiv was receiving from the West would not be used against targets in Russian territory.
Reznikov declined to confirm reports that he could soon be forced to resign following recent procurement scandals, saying the decision rested with President Volodymyr Zelensky, who last week stepped up efforts to clamp down on corruption.
"The stress that I have endured this year is hard to measure precisely. I am not ashamed of anything," he said. "My conscience is absolutely clear."
Reznikov, a lawyer by training, said he "will definitely find an interesting project for myself that will allow us not only to win the war, but also to punish the military and political leadership of the Russian Federation later."
The Ukrainska Pravda news website, citing unidentified sources, reported that Reznikov, 56, could next week be replaced by Kyrylo Budanov, the 37-year-old head of military intelligence.
One of the best-known faces of Ukraine's war effort, Reznikov was appointed defence minister in November 2021 and has helped secure Western weapons to buttress Ukrainian forces.
But his ministry has been beset by corruption scandals.
Reznikov's deputy was forced to resign in late January after the ministry was accused of signing food contracts at prices two to three times higher than current rates for basic foodstuffs. Reznikov said Sunday that an internal audit of procurement procedures was under way.
The ministry's own anti-corruption department "failed" to accomplish its tasks and needs to "be completely rebooted," Reznikov said.
In the deserted eastern town of Bakhmut, about 20 people, including two soldiers, attended a Sunday mass in the basement of the golden-domed All Saints' church.
Three women sang hymns, punctuated by sounds of mortar shells in the background.
The room was lit by two dozen candles and a portable light used by the two priests to read from the bible.
"Today I prayed that everything will be better for me after I die," said 20-year-old Serafim Chernyshov, standing outside the church, with loud sounds of a steady exchange of small arms fire and the pounding of mortar shells to and from Russian positions echoing in the background.
"Last night, a missile flew into my garden and a bullet flew inside my house, it could have hit me," he added. "I might die now or in 30 years. If I'm killed, it will be God's will."
"I came to pray for peace," added Lyubov Avramenko, 84.
Zelensky said on Friday that Kyiv's troops would fight for Bakhmut "as long as we can."
The British defence ministry said on Sunday that over the past week, Russia had made "small advances" in its attempt to encircle Bakhmut.
For months Moscow has targeted Ukraine's civilian infrastructure, including the energy grid, leaving millions in the dark and cold in the middle of winter.
In Kharkiv, Ukraine's second-largest city, a missile strike hit a residential building on Sunday, wounding four people, said Oleg Synegubov, head of the regional administration. Another strike left a security guard injured when a missile hit a university, he said.
On Saturday, "the Russians killed four residents of the region of Donetsk," said Pavlo Kyrylenko, head of the regional administration, adding that another 11 people were injured.
Around 280,000 households in the southern city of Odesa were still without power following an accident at an electrical substation, already damaged by Russian strikes, the day before, said Prime Minister Denys Shmygal.