US President Barack Obama, right, meets with Ukraine president-elect Petro Poroshenko in Warsaw, Poland, on Wednesday. — AP

WARSAW — President Barack Obama Wednesday condemned Russia’s “dark tactics” and bullying in Ukraine and President Vladimir Putin hit back at American “aggression,” as new venom deepened the worst US-Russia clash in decades.

Obama met Ukraine’s president-elect Petro Poroshenko in Warsaw and promised years of US support, then blasted Russia and vowed to protect ex-Soviet states in NATO in a hawkish speech marking 25 years of Polish democracy.

“How can we allow the dark tactics of the 20th century to define this new century?” Obama asked, as he adopted the mantle of ‘leader of the West’ worn by previous presidents during the Cold War.

“As we’ve been reminded by Russia’s aggression in Ukraine, our free nations cannot be complacent in pursuit of the vision we share – a Europe that is whole and free and at peace,” said Obama who spoke behind bullet proof glass in front of the Royal Castle in Warsaw – a rebuilt symbol of Polish triumph over the destruction and tyranny of the 20th century.

Obama will come face-to-face with Putin on Friday in France. Though several European leaders are meeting the Russian leader and hope to pursue dialogue to ease the Ukraine crisis – which saw hundreds of rebels battle government forces Wednesday – Washington remains to be convinced.

“We will not accept Russia’s occupation of Crimea or its violations of Ukraine’s sovereignty,” Obama said, as Defense Secretary Chuck Hagel announced in Brussels a review of “the US force presence in Europe” amid the Ukraine crisis.

“Our free nations will stand united so that further Russian provocations will only mean more isolation and costs for Russia,” Obama said in Warsaw, hours before arriving in Belgium later Wednesday for a G7 summit dedicated to coordinating policy towards Moscow.

In a clear reference to Russia’s action in Crimea and wider Ukraine, Obama warned that “the days of empires and spheres of influence are over.”

“Bigger nations must not be allowed to bully the small, or impose their will at the barrel of a gun or with masked men taking over buildings.”

Putin said he could not understand why Obama, who has spent months trying to isolate him over Ukraine, would not hold a formal meeting with him during 70th anniversary commemorations of the Normandy landings in World War II.

“It is his choice, I am ready for dialogue,” Putin said in an interview with French broadcasters Europe1 and TF1 conducted at his dacha in the Black Sea resort of Sochi.

The Russian leader accused the United States of hypocrisy in its “aggressive” attempts to punish Russia over Ukraine.

Unlike Obama, German Chancellor Angela Merkel, French President Francois Hollande and British Prime Minister David Cameron will meet one-on-one with Putin in France – reflecting their nations’ greater exposure to Russian economic power.

Obama met Poroshenko days before his inauguration and declared himself “deeply impressed” by the chocolate tycoon Ukrainians chose on May 25 to lead them back from a political and economic precipice. “The United States is absolutely committed to standing behind the Ukrainian people not just in the coming days, weeks, but in the coming years,” Obama told reporters.

In Ukraine, three government soldiers were injured in a massive all-night attack carried out by hundreds of pro-Russian insurgents in the nation’s restive east, authorities in Kiev said Wednesday.

The assault on a position held by the Ukrainian National Guard in the Lugansk region began Tuesday evening and lasted 10 hours, the interior ministry said, adding that six rebels were killed in the fighting.

The 300 rebels who took part in the attack were armed with automatic weapons, rocket launchers and mortars, and the Ukrainian forces fought “to the last bullet,” according to the ministry.

Washington accuses Moscow of coordinating and directing the rebels, and says continued fighting should merit tough new economic sanctions.

NATO defense ministers Tuesday agreed a series of steps to bolster protection in eastern Europe after the Ukraine crisis, but insisted they were acting within the limits of a key post-Cold War treaty with Moscow.

Obama meanwhile proposed a one-billion-dollar fund to finance new US air, naval and troop rotations through Eastern Europe, launching his regional tour designed to bolster NATO resolve and capacity against Moscow. — AFP