KIEV - Ukrainian President Volodymyr Zelensky vowed there would be no let-up in fighting to regain territory lost to Russia, as Kyiv reported its troops have advanced to the eastern bank of the Oskil River, threatening Russian occupation forces in the Donbas.
Crossing the Oskil is another important milestone in Ukraine's counter-offensive in the north-eastern Kharkiv region as it flows south to the Siversky Donets River, which goes right through Luhansk, one of two provinces in the Donbas region.
Ukrainian troops "have pushed across the Oskil. From yesterday, Ukraine controls the east bank", the Ukrainian Armed Forces wrote on Telegram late Sunday.
Mr Serhiy Gaidai, governor of the Luhansk region, wrote on Telegram: "Luhansk region is right next door. Decoccupation is not far away."
Mr Zelensky vowed to keep up the pressure on Moscow after Ukraine's rapid gains in Kharkiv this month.
"Perhaps it seems to some of you that after a series of victories we now have a lull of sorts," he said in his regular nightly address on Sunday. "But there will be no lull. There is preparation for the next series, for Ukraine must be free," he said. "All of it."
'They're defeating Russia'
US President Joe Biden also said victory for Ukraine meant removing Russian forces from the entire country, and pledged US support for as long as it takes.
"Winning the war in Ukraine is to get Russia out of Ukraine completely and to recognise the sovereignty. They're defeating Russia," he said in an interview on CBS' 60 Minutes programme that was broadcast on Sunday.
"Russia's turning out not to be as competent and capable as many people thought they were going to be," he said.
Russian artillery pounded towns and villages across the frontlines in the east and south on Sunday, including civilian infrastructure in Zaporizhzhia city, Ukrainian officials said.
Britain said Russian forces have widened strikes on civilian infrastructure following battlefield setbacks and are likely to expand their targets further.
"As it faces setbacks on the front lines, Russia has likely extended the locations it is prepared to strike in an attempt to directly undermine the morale of the Ukrainian people and government," Britain's Defence Ministry said.
Ukraine's southern command said Monday strikes were also launched on a radar station near Kherson and on a pontoon crossing near Nova Kakhovka east of Kherson, where a Ukrainian counter-offensive has focused on taking out bridges across the Dnipro and Inhulets Rivers.
Putin, Biden warnings
On Friday, Russian President Vladimir Putin brushed off Ukraine's swift counter-offensive, and said Moscow would respond more forcefully if its troops are put under further pressure.
Such repeated threats have raised concerns Mr Putin could, at some point, turn to small nuclear weapons or chemical warfare.
Mr Biden, asked what he would tell Mr Putin if he was considering using such weapons, replied in the 60 Minutes interview: "Don't. Don't. Don't. It would change the face of war unlike anything since World War Two."
Some military analysts have said Russia may also stage a nuclear incident at the Zaporizhzhia nuclear power plant held by Russia but run by Ukrainian staff. Moscow and Kyiv have accused each other of shelling around the plant that has damaged buildings and disrupted power lines needed to keep it cooled and safe.
US Army General Mark Milley, chairman of the Joint Chiefs of Staff, called for vigilance Sunday after visiting a base in Poland aiding Ukraine's war effort.
"The war is not going too well for Russia right now, so it's incumbent upon all of us to maintain high states of readiness, alert," he said after his trip to the base, which reporters travelling with him were asked not to identify.
With its battlefield losses mounting, the Russian army is seeking contract soldiers for what it calls the "special military operation" in Ukraine, and is offering nearly US$3,000 (S$4,200) a month as an incentive.
A special unit stationed a recruitment truck in the southern city of Rostov on the weekend, and masked soldiers handed out brochures titled "Military service on a contract - the choice of a real man".
On Saturday, Mr Zelensky said the authorities found a mass grave containing the bodies of 17 soldiers in Izyum, some of which he said bore signs of torture.
Izyum residents have been searching for dead relatives at a forest grave site where workers began exhuming bodies last week.
Ukrainian officials said last week they found 440 bodies in woods near Izyum. They said most of the dead were civilians and the causes of death had not been established.
The Kremlin has not commented on the discovery of the graves, but in the past Moscow has repeatedly denied deliberately attacking civilians or committing atrocities. REUTERS