Ukrainian forces have beaten back Russian units to control about half of the flashpoint eastern city of Severodonetsk, according to local officials. President Volodymyr Zelensky has, meanwhile, been visiting the front lines to support Ukraine's "true heroes".
As the struggle continued for control of the strategically important city of Severodonetsk -- the largest in the Lugansk region not under Russian control -- more help was promised from abroad.
The United Kingdom said it would follow the United States and send long-range missile systems to Ukraine, defying warnings from Russian President Vladimir Putin against supplying Kyiv with the advanced weapons.
Fighting since April has been concentrated in the east of the country, where Russian forces have made slow but steady advances after being beaten back from other parts of Ukraine, including the capital Kyiv.
Ukraine's gains in Severodonetsk, announced by regional governor Sergiy Gaiday, represent a significant advance by Kyiv's troops, who had been on the verge of being driven out of the city.
"The Armed Forces have cleared half of Severodonetsk and are moving forward," Gaiday posted on Telegram.
However, he warned in a video in the same post that a major new Russian offensive appeared imminent.
President Zelensky praises army
President Volodymyr Zelensky on Sunday visited the defensive front line near Severodonetsk.
The Ukrainian leader was in the southwest in the Donetsk region of the Donbas to talk with servicemen.
"I want to thank you for your great work, for your service, for protecting all of us, our state. I am grateful to everyone," he told them.
"I am proud of everyone whom I met, whom I shook hands with, with whom I communicated, whom I supported," Zelensky said in his daily evening address after his visit.
"Each family has its own story. Most were without men," he said.
"Someone's husband went to war, someone's is in captivity, someone's, unfortunately, died. A tragedy. No home, no loved one. But we must live for the children. True heroes -- they are among us."
Kyiv again hit by Russian missiles
Sunday also brought the first Russian missile strikes on Kyiv since 28 April.
"High-precision, long-range missiles fired by the Russian Aerospace Forces on the outskirts of Kyiv destroyed T-72 tanks supplied by eastern European countries and other armoured vehicles that were in hangars," a Russian defence ministry spokesman said.
Ukraine has asked supporting countries for ever-more powerful arms to fend off the Russian attack.
The United States last week said it would supply Ukraine with advanced missile systems, the latest in a long list of weaponry sent or pledged to the pro-Western country.
But Russian President Vladimir Putin said long-range missile supplies to Ukraine meant "we will draw the appropriate conclusions and use our arms ... to strike targets we haven't hit before".
UN efforts to facilitate wheat exports
Russian troops now occupy a fifth of Ukraine's territory, according to Kyiv, and Moscow has imposed a blockade of Ukrainian Black Sea ports, sparking fears of a global food crisis.
Ukraine and Russia are among the world's leading exporters of wheat.
The United Nations said it was leading intense negotiations with Russia to allow Ukraine's grain harvest to leave the country.
