Ukrainian forces have retaken two more cities in the east from separatist rebels, a day after recapturing Slovyansk, President Petro Poroshenko said on his Web site.

The BBC said the announcement on the retaking of Artyomivsk and Druzhkivka came as pro-separatist demonstrators rallied in Donetsk, waving Russian flags and those of the Donetsk People's Republic. They called on Russian President Vladimir Putin to come to their aid.

RT reported government artillery was unleashed on Luhansk and aircraft flew sorties over the city's suburbs.

"My order is now in effect -- tighten the ring around the terrorists," Poroshenko tweeted on Sunday. "Continue the operation to liberate Donetsk and Luhanskregions," he said, naming Ukraine's two major eastern parts which have boiled with separatist rebellion since April. Reuters reported Poroshenko called the recapture of Slovyansk a turning point in the conflict.

Rebel forces were reported regrouping in Donetsk after abandoning Slovyansk Saturday. Ukraine's prison service said rebels destroyed guard headquarters in Donetsk in a bid to capture weapons, Interfax-Ukraine reported.

Meanwhile the National Security and Defense Council has prepared a declaration of martial law for Donetsk and Luhansk.

"I do not rule out that there may come a time when it will prove necessary to declare martial law," Council Secretary Andriy Parubiy told a Friday press briefing.