French President Francois Hollande and German Chancellor Angela Merkel were expected to push the Western-backed leader on a ceasefire in three-way telephone talks but Kiev has until now shrugged off calls to halt an offensive that has reclaimed a string of key rebel towns.
Dressed in military fatigues Poroshenko yesterday made a triumphant visit to the vanquished rebel bastion of Slavyansk where government troops raised the national flag last week after pro-Moscow insurgents fled in the face of a fierce onslaught.
The resurgent leader promised to win back "very soon" the regional capitals of Donetsk and Lugansk but the rebels are digging in and have pledged to battle on.
Ukraine's military says it controls all routes in and out of the cities and a spokesman for Kiev's National Security and Defence Council warned a plan was in place that would give the rebels an "unpleasant surprise."
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In Donetsk -- an industrial city of some 1 million people -- fears are mounting among the population that the mining hub will face clashes similar to the ones that gutted the city's airport in May.
Rebel military chief Igor Strelkov -- whom Kiev accuses of being a Moscow intelligence operative -- said fighters were working to reinforce the weak defences around Donetsk and bolster their numbers.
"We are taking urgent measures to prepare Donetsk for battle," Stelkov was reported as telling the insurgent's TV station Wednesday by Russia's state ITAR-TASS news agency.
Poroshenko -- who signed a historic political and trade deal with the EU last month -- tore up a 10-day ceasefire on July 1 because of uninterrupted rebel attacks that claimed the lives of more than 20 Ukrainian troops.