Smoke rises after an airstrike, as Russia's attack on Ukraine continues, in Lviv, Ukraine. File/Reuters
"Several explosions in Darnytskyi and Dniprovskyi districts of the capital," Kyiv Mayor Vitali Klitschko wrote on the Telegram messaging app. "Services are already working on site. The media witness saw smoke in the city after the explosions.
The Ukrainian claim on Sievierodonetsk could not be independently verified, and Moscow said its own forces were making gains there. But it was the first time Kyiv has claimed to have launched a big counter-attack in the small industrial city after days of yielding ground.
Sievierodonetsk Mayor Oleksandr Stryuk said street fighting continued during the day on Saturday, with both sides exchanging artillery fire.
Several explosions in Darnytskyi and Dniprovskyi districts of the capital.
"The situation is tense, complicated," he told national television, saying there was a shortage of food, fuel and medicine. "Our military is doing everything it can to drive the enemy out of the city."
Russia has concentrated its forces on Sievierodonetsk in recent weeks for one of the biggest ground battles of the war, with Moscow appearing to bet its campaign on capturing one of two eastern provinces it claims on behalf of separatist proxies.
Both sides claim to have inflicted huge casualties in the fighting, a battle that military experts say could determine which side has the momentum for a prolonged war of attrition in coming months.
In the diplomatic sphere, Kyiv rebuked French President Emmanuel Macron for saying it was important not to "humiliate" Moscow.
Arkadiy Maznychenko, a 75 year-old-retiree, reacts outside his destroyed house in Horenka, Kyiv. AFP
"We must not humiliate Russia so that the day when the fighting stops we can build an exit ramp through diplomatic means," Macron told regional newspapers in an interview published on Saturday, adding he was "convinced that it is France's role to be a mediating power."
Ukrainian Foreign Minister Dmytro Kuleba tweeted in response: "Calls to avoid humiliation of Russia can only humiliate France and every other country that would call for it.
"Because it is Russia that humiliates itself. We all better focus on how to put Russia in its place. This will bring peace and save lives."
Ukrainian President Volodymyr Zelensky offered a stark message: "The terrible consequences of this war can be stopped at any moment ... if one person in Moscow simply gives the order," he said, in an apparent reference to Russian President Vladimir Putin. "And the fact that there is still no such order is obviously a humiliation for the whole world."