Ukraine's president has called the capture of the Pro-Russian separatist stronghold of Slovyansk a "turning point" in the fight for control of the country's east.
Petro Poroshenko's comments on Sunday came as Russia's state news agency, quoting Ukrainian officials, said Kiev was planning to launch major offensives in the regions of Donetsk and Luhansk.
"My order is now in effect - tighten the ring around the terrorists," Poroshenko said on Twitter on Sunday. "Continue the operation to liberate Donetsk and Luhansk regions," he said, naming Ukraine's two major eastern regions affected by a Pro-Russian rebellion since April.
"This is not full victory. But the clearing out of people armed to the teeth from Slovyansk has huge symbolic importance. It is the beginning of the turning point in the battle with fighters for the territorial integrity of Ukraine," Poroshenko said.
He acknowledged the rebels were regrouping in other towns. "There are further tests ahead."
Thousands of pro-Russian supporters demonstrated on Sunday in Donetsk to show their support for separatists driven from their stronghold of Slovyansk the day before.
Pro-Russia separatists regrouped in the contested region, and told thousands of cheering supporters they would renew their fight against Kiev.
A female protester carrying an anti-Ukrainian army sign said she wanted Russia's help because the separatists could not make it on their own.
There were no immediate figures for casualties caused by the government offensive in Slovyansk, launched after Poroshenko refused to renew a unilateral ceasefire and ordered the resumption of a government offensive on June 30.
Slovyansk had put up some of the fiercest resistance to Ukrainian forces, bringing down at least three military helicopters and one Antonov-30 plane.
Pro-Russian forces have been commanded by Igor Girkin, a Muscovite who was declared the defence minister of the self-proclaimed Donetsk People's Republic. Kiev says he is a veteran of the Russian military intelligence agency.
The city's capture is Kiev's most notable military victory in three months of fighting in which more than 200 Ukrainian troops have been killed.
Meanwhile, Girkin, who also uses the alias, Igor Strelkov, told the Russian television channel Life News on Sunday that he had arrived in Donetsk from Slovyansk.
Rebel fighters from Slovyansk and other towns taken over by the Ukrainian army were seen on Sunday milling around central Donetsk, the AFP news agency reported.
"We will continue the combat operations and will try not to make the same mistakes that we made in the past," said Girkin.