WARSAW (AFP) - President Barack Obama met Ukraine's president-elect Petro Poroshenko on Wednesday, in a show of US support for Ukraine's right to chart its own future, before an encounter with Russia's Vladimir Putin.
Obama sat down with Poroshenko in Warsaw, during a trip designed to assuage security concerns in eastern Europe following Russia's annexation of Crimea and what Washington says is an effort to destabilise Ukraine.
The talks on day two of Obama's European tour will come after the president met central and eastern European leaders in Warsaw and before he heads to a G7 summit in Belgium which is designed to cement Western policy towards Russia.
Obama will come face to face with Putin during 70th anniversary commemorations of the D-Day landings in Normandy, France on Friday.
The leaders of Britain, France and Germany will go a step further and hold one-on-one talks with Putin.
The accelerating diplomacy over Ukraine comes as a seven-week pro-Russian insurgency in Ukraine's eastern rust belt grows only more violent after Poroshenko swept to power in a May 25 presidential ballot.
Hundreds of separatist gunmen on Monday attacked a Ukrainian border guard service camp in the region of Lugansk on the border with Russia.
Obama said Tuesday that US commitment to eastern European security was absolute.
"Our commitment to Poland's security as well as the security of our allies in central and eastern Europe is a cornerstone of our own security and it is sacrosanct," Obama said after inspecting a joint unit of Polish and US F-16 pilots.
He proposed a "European Reassurance Initiative" of up to US$1 billion (S$1.26 billion) to finance extra US troop and military deployments to "new allies" in Europe.
NATO defence ministers also agreed Tuesday 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 met Poroshenko Wednesday as the confectionery tycoon faces the unenviable task of keeping his economically ravaged country from slipping into an all-out civil war that Washington blames Moscow for orchestrating.
"Events in Ukraine have unfortunately unleashed forces that we had all hoped had been put away, were behind us," US Secretary of State John Kerry said in Warsaw.
In eastern Ukraine, rebels pelted the border guard camp with mortar fire and deployed snipers on rooftops surrounding the base in a day-long battle that marked one of their most brazen offensives of the campaign.
Ukraine's military reported no fatalities but said they had killed five rebels.
A defence spokesman said two Ukrainian soldiers were killed and 42 wounded in new violence that swept the neighbouring coal mining province of Donetsk on Tuesday.
Washington's commitment to Ukraine will be reinforced when US Vice President Joe Biden travels to Kiev on Saturday to attend Poroshenko's swearing-in as the country's fifth post-Soviet president.
Kiev has refused to invite Putin to the inauguration because of his failure to formally recognise the May 25 vote's outcome or rein in the separatist campaign.
Ukraine and its eastern European allies such as Poland have been pushing the West to unleash painful economic sanctions against entire sectors of Russia's economy in response to the Kremlin's perceived support of the rebels.
Obama addressed those calls directly by telling a joint press conference with his Polish counterpart Bronislaw Komorowski that Russia faced further punitive measures unless it put restraints on the separatists.
"Further Russian provocation will be met with further costs for Russia including, if necessary, additional sanctions," Obama said.
On Friday, Obama will attend 70th anniversary commemoration of the D-Day landings in Normandy which Putin will also attend.
The US leader has spent months trying to isolate his rival and punish the Kremlin's inner circle with sanctions that have cut it off from access to US and many Western banks.
Both the Kremlin and White House say Obama and Putin have no plans to meet for one-on-one talks.
Obama on Tuesday called on Putin to accept Poroshenko's invitation to hold talks in Normandy. If he agrees, it would be Putin's first meeting with a Ukrainian leader since the February ouster of Kremlin-backed president Viktor Yanukovych set Kiev on its new westward course.