Ukraine handed out aid in a battle-scarred town after driving back Russian forces in the northeast and vowed to free all of its territory, calling on the West to speed up deliveries of weapons to back the dramatic advance.
Since Moscow abandoned its main bastion in northeastern Ukraine on Saturday, marking its worst defeat since the early days of the war, Ukrainian troops have recaptured dozens of towns in a stunning shift in battleground momentum.
In Washington, the White House said the United States was likely to announce a new military aid package for Ukraine in "coming days".
Speaking in the central square of Balakliia, a crucial military supply hub taken by Ukrainian forces late last week, Ukraine's Deputy Defence Minister Hanna Malyar said 150,000 people had been liberated from Russian rule in the area.
Ukrainian flags had been raised and a large crowd gathered to receive bundles of humanitarian aid. A shopping centre had been destroyed but many buildings remained intact, with shops closed and boarded up.
Maria Tymofeeva, 43, said fighting had raged for three days last week before going quiet.
"A lot of people have disappeared," she said. Asked if there were many collaborators in the town, she said, "I think so, yes", before adding, with a laugh, "I think they have fled!"
Fighting was continuing elsewhere in the northeastern Kharkiv region, Malyar earlier told Reuters, saying Ukraine's forces were making good progress because they were highly motivated and their operation well planned.
"The aim is to liberate the Kharkiv region and beyond - all the territories occupied by the Russian Federation," she said on the road to Balakliia, which lies 74km southeast of Kharkiv, Ukraine's second largest city.
In Verbivka, a village northwest of Balakliia, Nadia Khvostok, 76, described the traumatic occupation and the arrival of Ukrainian troops, saying residents greeted them "with tears in our eyes".
"We could not have been happier. My grandchildren spent two and a half months in the cellar. When the corner of the house was torn off, the children began to shudder and stutter," she said, adding that they and her daughter had left - she did not know where.
The village school, where the Russians were based, was destroyed and trees on the road to the village and a cement factory showed battle scars. Elsewhere were abandoned Russian vehicles, including a military truck with a smashed windscreen.
Kharkiv regional governor Oleh Syehubov, who came to Verbivka, said the authorities were trying to record crimes committed by Russians during their occupation of the area, and recover the bodies of victims.
"We're asking everyone around about all the places of burial which can be found," he said. "We have found some places of the burial of civilians. We are continuing with the process of exhumation. So far we know of at least five people, but unfortunately this is not the end, believe me."
Moscow denies its forces have committed atrocities in areas they have controlled.
Ukraine's military accused retreating Russian soldiers of stealing at least 300 private cars loaded with looted property as they fled the region. The Russian defence ministry did not immediately reply to a request for comment.
During the day, Ukrainian forces repelled enemy attacks in six towns and settlements to the north of Donetsk, the general staff said, but made no mention of captured territory.
In a video address, President Volodymyr Zelenskiy said the West must speed up deliveries of weapons, calling on allies to "strengthen cooperation to defeat Russian terror".
Foreign Minister Dmytro Kuleba singled out Germany for refusing to provide tanks and armour: "Not a single rational argument on why these weapons cannot be supplied, only abstract fears and excuses. What is Berlin afraid of that Kyiv is not?"
Russian forces still control about a fifth of Ukraine in the south and east, but Kyiv is now on the offensive in both areas.
With the recapture of nearly all of Kharkiv province, the Ukrainian advance could soon spread into neighbouring Luhansk and Donetsk, where Russia has concentrated its forces for months to expand territory held by separatists since 2014.
The Ukrainian governor of Luhansk, Serhiy Gaidai, said troops had already retaken the city of Lyman in northern Donetsk. He identified Svatove in Luhansk further east as the likely next battle front. Reuters could not verify the reports.
A senior US military official said Russia had largely ceded territory near Kharkiv in the northeast and pulled many of its troops back over the border.
A video from Ukraine's border guard service showed what it said were Ukrainian troops liberating the town of Vovchansk near the Russian border, burning down flags and tearing down a poster saying "We are one with Russia".
Zelenskiy said Ukraine had recaptured roughly 6000 square km of territory, double the area officials had cited on Sunday.
Another ex-Soviet conflict
Fighting broke out between two other former Soviet republics on Monday, raising fears of another conflict. Azerbaijan, which is backed by Turkey, and Armenia, an ally of Russia, blamed each other for the clashes, with each reporting about 50 dead.
Russia maintains peacekeepers in the area as guarantor of an agreement that ended a war there two years ago. Some analysts said the fighting could have resumed in part because Russia's military is now tied up in Ukraine. The Kremlin said Russian President Vladimir Putin was trying to end the clashes.
Kremlin spokesperson Dmitry Peskov said there was no discussion of a nationwide mobilisation in Russia to bolster the operation in Ukraine, which he has said will continue until it achieves its goals.
Since the past week's losses, Russian nationalist commentators online have become increasingly critical of the conflict's conduct, many demanding mobilisation. Peskov called that an example of "pluralism", adding that Russians as a whole continue to support Putin.
- Reuters