Fighting raged for the strategic Ukrainian city Lysychansk on Saturday, as Belarusian leader Alexander Lukashenko said his army had intercepted missiles fired on his territory by Kyiv's forces.
Ukraine denied claims by Moscow-backed separatists who said they had encircled Lysychansk, the last major city in the Lugansk area of the eastern Donbas region still in Kyiv's hands.
On Saturday, the pro-Russian separatists had already announced the capture of Lysychansk, to which Kiev replied that the strategically important city was still under its own control.
Ukraine also admitted Russian gains in the territory.
"In the Donetsk region, the occupiers are concentrating on consolidating their positions in the towns of Lysychansk and Verkhnyokamyanka," the Ukrainian General Staff announced on Sunday.
The Ukrainian military governor of the Luhansk region, Serhiy Hajdaj, confirmed on his Telegram channel that Russian troops had "gained a foothold in the Lysychansk district."
It is unclear whether Ukrainian units remain in the city.
Lysychansk was the last large Ukrainian-controlled town in the Luhansk region after the fall of Severodonetsk.
The city's capture would allow Russian forces to push deeper into the Donbas, which has become the focus of their offensive since failing to capture Kyiv.
"Fighting rages around Lysychansk... The city has not been encircled and is under control of the Ukrainian army," Ruslan Muzytchuk, a spokesman for the Ukrainian National Guard, said on Ukrainian television.
Earlier in the day, Andrei Marochko, a spokesman for the separatist forces, told the TASS news agency: "Lysychansk is completely encircled."
Lukashenko on Saturday accused Ukraine of "provoking" neighbouring Belarus, saying his army intercepted missiles fired at his country by Ukrainian forces "around three days ago".
The claim came one week after Ukraine said missiles struck a border region from Belarus, a long-term Russian ally that supported the February 24 invasion.
But Lukashenko denied any involvement, which would represent an escalation of the conflict.
"As I said more than a year ago, we do not intend to fight in Ukraine," he was quoted as saying by state news agency Belta on Saturday.
Lukashenko also used a speech on Saturday to threaten military retaliation against anybody who attacked his country, as tensions over the war in neighbouring Ukraine remained high.
Speaking on the eve of the country's Independence Day, Lukashenko said that he had ordered his armed forces to target "the decision-making centres" of Western capitals in the event of an attack on Belarus, adding: "Don't touch us - and we won't touch you," according to state news agency Belta.
Despite the fact that it was Russia that invaded Ukraine, Moscow and its staunch ally Minsk have repeatedly attempted to portray themselves as victims of supposedly hostile Western and NATO policies.
There have been fears that Belarus could officially enter the war alongside Russia since the Ukraine conflict began in late February, with Lukashenko admitting that Russian missiles were fired at Ukraine from Belarusian territory in the first weeks of the invasion.
At its two-day summit in Madrid earlier this week, NATO decided to significantly strengthen its eastern flank and to begin the process of admitting Finland and Sweden to the defence alliance.
Russian President Vladimir Putin then announced his intention to respond to the possible transfer of NATO soldiers to Finland with proportional Russian troop deployments in the region.
