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As fighting raged around the rebel strongholds of Donetsk and Luhansk, the Ukrainian leader awarded members of the newly formed National Guard with medals for service.
"This is a real fight for the sovereignty of Ukraine, the territorial integrity of Ukraine, for the independence of Ukraine," said Poroshenko, wearing military camouflage.
"It is not an internal conflict, it is Ukraine defending its territory from foreign mercenaries, from bandits and from terrorists," he told soldiers.
Kiev has accused Moscow of sending the rebels fighters and weapons across its porous border with Ukraine, a charge Russia denies. But some battalions have openly said they were made up of volunteers from various countries, including Russia.
Ukraine's army has forced the rebels back towards the cities of Donetsk and Luhansk, where the separatists have boosted their defences, and fighting has raged since a Malaysian airliner was downed last week.
Shelling and explosions were heard around rebel-held Donetsk on Saturday, and many shops were shuttered as Ukrainian forces pressed their military campaign against pro-Russian separatists.
"Last night was terrible. I was woken up at 3am by the explosions. The walls shook, the windows shook," said Marina, who lives in a southern part of the city.
"There was shooting all over the city. And it still goes on. Maybe it's a little quieter now, but it's all around."
Local officials said some buildings had been damaged, one by fire, and one woman was wounded.
In Luhansk, rebels said at least 19 civilians had been killed in fighting overnight and local officials said 60 percent of the city was left with no electricity after power lines were damaged.
Kiev's troops have also advanced from the south and their frontline checkpoint on a road from the Azov Sea city port of Mariupol now sits some 10 kilometres outside of Donetsk.