Ukraine’s military says its forces have retaken over 3,000 sq km (1,158 sq miles) during a rapid counter-offensive in eastern Ukraine.
The remarkable advance, if confirmed, means Kyiv’s forces have tripled their stated gains in little over 48 hours.
On Thursday evening, President Zelensky put the figure at 1,000 sq km, and then 2,000 sq km on Saturday evening.
The BBC cannot verify the Ukrainian figures, and journalists have been denied access to the frontlines.
On Saturday, the eastern counter-attack saw Ukrainian troops enter the vital Russian-held supply towns of Izyum and Kupiansk.
But UK defence officials have warned that fighting has continued outside those towns. And officials in Kyiv said Ukrainian forces were still fighting to gain control of a number of settlements around Izyum.
Russia’s defence ministry confirmed its forces’ retreat from Izyum itself and Kupiansk, which it said would allow them”to regroup” in territory held by Moscow-backed separatists.
The Russian ministry also confirmed the withdrawal of troops from a third key town, Balaklyia, in order to “bolster efforts” on the Donetsk front. Ukrainian forces entered the town on Friday.
The pace of the counter-attack has caught the Russians off guard, and Chechen leader Ramzan Kadyrov – a staunch supporter of President Vladimir Putin – appeared to question Moscow’s military strategy.
In a message posted to Telegram, Mr Kadyrov said if there was not a change in Russia’s fortunes, he would be forced to question the country’s leadership to explain the situation.
On Saturday, the head of the Russia-installed administration in the Kharkiv region recommended that its people evacuate to Russia “to save lives”.
Unverified footage on social media appeared to show long queues of traffic building up at border crossings. The governor of the Belgorod border region in Russia, Vyacheslav Gladkov, said “thousands” of people had crossed into the country.
Meanwhile, Gen Valerii Zaluzhnyi, commander of Ukraine’s military, said his forces had advanced to within 50km (31 miles) of the Russian border.
But Russians still hold around a fifth of the country, and few imagine a swift end to the war.
In an interview with the Financial Times, Ukraine’s defence minister Oleksii Reznikov hailed his troops, but warned of the potential for a Russian counter-attack.
“A counter-offensive liberates territory and after that you have to control it and be ready to defend it,” Mr Reznikov said. “Of course, we have to be worried, this war has worried us for years.”