Also present at the observance will be Russian President Vladimir Putin, but there are no indications yet that there will be a direct meeting between the two – the first such opportunity since Poroshenko’s overwhelming election win last Sunday.
Relations between Ukraine and Russia deteriorated following the ouster of Moscow-backed president Viktor Yanokovych in February following months of protests, and Russia’s annexation of Ukraine’s Crimea in March.
Condemning the takeover of the peninsula as an illegal land-grab, Kiev also accuses Moscow of fomenting separatist unrest in eastern Ukraine, which to date has claimed dozens of lives and raised internal tensions.
Should the two men come face-to-face it would be the first time Russia's president would meet an official of Ukraine’s new pro-Western government.
Putin and Poroshenko are among several leaders including U.S. President Barack Obama, German Chancellor Angela Merkel and Polish President Bronislaw Komorowski - all key players in the Ukraine crisis - who are due to meet for lunch on June 6 to mark D-day.
Uneasy calm in Ukraine's east
Some calm returned to Ukraine’s east on Wednesday, a day after government troops, in one of their biggest shows of force to date, killed as many as 50 pro-Russia separatists in the country’s restive Donetsk region.
The operation, which was centered on retaking control of Donetsk International Airport seized by rebels earlier, came after Ukrainians, in a poll on Sunday, overwhelming elected pro-Western chocolatier and former foreign minister Petro Poroshenko as their new president.
The assault, following weeks of restraint, filled morgues in the region’s eponymous capital with bodies of rebel gunmen, some with limbs missing.
Pro-Moscow gunmen have declared the city of a million people capital of an independent "Donetsk People's Republic" they proclaimed following a referendum condemned by both Kiev and the West.
Some battles between separatists and Ukrainian government forces Wednesday in the region of Luhansk.
Ukraine's Interior Ministry reported that the fighting broke out when separatist fighters tried to overrun a Ukrainian National Guard unit in the city of Luhansk.
The ministry said there were losses on both sides but provided no casualty figures.
Obama blasts Russia, praises allies
President Obama on Wednesday again condemned Russia for its “aggression” against Ukraine and praised Western allies for their unified response to the crisis.
In a speech on global challenges and America’s role in the world, Obama said that Moscow’s posturing brought back memories of “the days when Soviet tanks rolled into Eastern Europe.”
He praised Western allies and organizations for uniting behind Ukraine in the face of Russia’s actions.
“This mobilization of world opinion and institutions served as a counterweight to Russian propaganda, Russian troops on the border, and armed militias,” said Obama speaking at a commencement ceremony at the U.S. Military Academy at West Point, New York.
“Standing with our allies on behalf of international order has given a chance for the Ukrainian people to choose their future,” added Obama in remarks before hundreds of cadets.
Russian Foreign Minister Sergei Lavrov on Wednesday accused the West of pushing Ukraine into a “fratricidal war” and repeated Moscow's calls for an end to Kiev’s “punitive operations” in the country’s east.
Lavrov’s remarks echoed earlier Russian statements placing blame on the United States and the EU for the turmoil in Ukraine.
“The people [of Ukraine] are in essence being pushed into the abyss of fratricidal war,” Russian news agencies quoted Lavrov as saying at a ministry reception attended by the head of the Russian Orthodox Church, Patriarch Kirill.
Ukrainian Prime Minister Arseniy Yatsenyuk called on Russia's Vladimir Putin on Wednesday to block the border to Ukraine to prevent separatist fighters from entering the country.
He said that if Russian influence was eliminated, the crisis could be ended swiftly.
Yatsenyuk accused Moscow of supporting, financing and providing rebels access to Ukrainian territory.
Also Wednesday, several hundred coal miners from the Donetsk region rallied in support of pro-Russia militants.
The miners marched through Donetsk city center to demand the withdrawal of Ukrainian forces from the region.
The protesters carried "Donetsk People's Republic" flags and banners reading “We will revive the power of the Donbass," a reference to Ukraine's industrial heartland.
According to Ukrainian media reports, the workers belong to a miners union closely associated with ousted president Yanukovych's Party of Regions.
Other unions seemed to have distanced themselves from the rally.
Source: Voice of America