At least two people are reported dead after a mini-bus was hit during shelling in Eastern Ukraine.
Eight others are said to be injured after the incident in Luhansk, which the Ukrainian authorities have blamed on separatists.
Government forces say thay have been making gains in recent days, in their battle with the pro-Russian rebels.
They have regained control of several areas in eastern Ukraine. President Poroshenko said the national flag had been hoisted over Artemivsk and Druzhkivka in the Donetsk region. His office added that the town of Kostiantynivka in the same region had also been retaken.
The separatists continue to hold three towns in the east: Donetsk, Horlivka and Luhansk.
Poroshenko, drawing confidence from the fall of the rebel bastion of Slovyansk at the weekend, has named a new chief of military operations in the east.
A security official said the government’s plan to clear rebels from the two big towns of Donetsk and Luhansk would come as a “nasty surprise” for the insurgents.
Military officials have been displaying weapons left behind by insurgents when they left Slovyansk – one of the towns retaken by the Ukrainian army.
The Defence Minister Valeriy Heletey has said Kyiv will only negotiate with the rebels once they lay down their arms.
He told reporters that the arms originated in Russia and were only brought to Ukraine after the conflict started three months ago.
Russian Foreign Minister Sergei Lavrov meanwhile, visiting Slovenia, has called for an immediate ceasefire. He said European countries should concentrate on ending the fighting rather than drawing up new blacklists of Russian officials.