The 48-year-old candy magnate -- dubbed the "chocolate king" -- delivered a forceful inauguration address the day before in which he vowed to pursue Ukraine's new pro-European course and never to accept Russia's annexation of Crimea.
He flatly rejected dialogue with "gangsters and killers" who have declared independence in two heavily-Russified eastern regions and are waging a bloody campaign against Ukrainian forces that Kiev and the West accuse the Kremlin of choreographing.
Europe's worst security crisis in decades has now plunged East-West relations into a Cold War-style standoff and left the ex-Soviet country of 46 million facing disintegration and economic collapse.
A Ukrainian military source told AFP that gunmen had staged a series of unsuccessful raids late yesterday and early today on an airport in the Russian-border city of Lugansk.
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The source said Ukrainian forces suffered no casualties but could not say if any militants had been killed.
"It is the first time we have had an attack of this kind," the soldier said by telephone.
The insurgents lost more than 40 fighters -- most of them Russian nationals -- while briefly seizing the main the international hub in the neighbouring industrial city of Donetsk in late May.
Yet the outlines of a possible solution to the crisis seemed in evidence on Friday when Russian President Vladimir Putin, nudged by German Chancellor Angela Merkel, held what he described as a brief but "very positive" meeting with Poroshenko during D-Day commemorations in France.
Putin appeared to respond to US pressure yesterday by demanding extra protection of Russia's western border in order to stem the flow of militants and weapons into Ukraine.
The seeming shift in Putin's aggressive approach prompted Poroshenko to indicate he might receive a top Russian envoy for talks today.