Poroshenko's efforts to quell the insurgency have been focused on encircling Donetsk, the largest rebel-controlled city. Fighting began in mid-April after Russia annexed Crimea, a peninsula on the Black Sea, while Kiev's forces have recaptured significant amounts of territory from the separatists.
Moscow has denied allegations by Kiev and the West that it has fomented the rebellion in eastern Ukraine. It says the Ukrainian government has discriminated against residents of the region who seek closer ties to Russia.
In fighting Tuesday, one soldier was killed and four wounded when a pro-Kiev battalion of volunteers came under mortar fire before entering the town of Ilovaysk, 11 miles east of Donetsk, Ukrainian officials said.
Ukrainian troops also captured a neighborhood in Luhansk as they battled rebels on the city's streets, National Security Council spokesman Andriy Lysenko said.
With the rebels losing more and more ground, the Kremlin announced a summit will be held Tuesday in Minsk, Belarus, that would also include top officials from Ukraine, the European Commission and the Customs Union bloc, which comprises Russia, Kazakhstan and Belarus. Putin and Poroshenko have not met since early June.
The conflict has recently taken a huge toll on Luhansk, a city near the Russian border that has been left without electricity, running water or phone service for 17 days. Central Luhansk came under fierce shelling overnight, killing and wounding civilians, the city administration said, without giving casualty figures. Residents were reported to be standing in lines to buy bread. Authorities also expressed fears about the possible outbreak of diseases from mounting piles of garbage that have been uncollected for more than two weeks.