* Obama and Poroshenko meet in Polish capital
* Ukraine president-elect is "wise choice"
* U.S. leader offers economic, security support
* Days of heavy fighting in eastern Ukraine
U.S. President Barack Obama endorsed Ukraine's president-elect Petro Poroshenko on Wednesday, offering Kiev financial and security help and saying he was the right choice to lead the country locked in a stand-off with Moscow.
At their first meeting since the billionaire confectionary magnate was elected last month against a backdrop of armed clashes in Ukraine's east, Obama said he was impressed by Poroshenko's vision for pulling his nation out of crisis.
"What Ukrainians said in the elections is that they reject that path. They reject violence," and want the opportunity to determine their own future, Obama told reporters after meeting Poroshenko in the Polish capital.
"That's the hope that President Poroshenko represents," Obama said. "In my discussions with him today it's clear he understands the hopes and aspirations of the Ukrainian people."
He said they had discussed Poroshenko's plans for restoring peace and order in Ukraine and reducing its dependence on Russia for energy. "I have been deeply impressed by his vision," Obama said.
Speaking after their talks, Poroshenko said he was ready to present a plan for "the peaceful resolution of the situation in the east" very soon after his inauguration on Saturday. He gave no details but he has backed a military crackdown on the rebels.
Known to some Ukrainians as the "chocolate king", Poroshenko won a May 25 presidential election called after the previous Kremlin-backed head of state, Viktor Yanukovich, fled to Russia in February after an uprising against his rule.
Russia seized control of Ukraine's Crimean peninsula, home to Moscow's Black Sea fleet, and annexed it in March, sparking the most severe east-west crisis since the end of the Cold War.
Poroshenko takes over a country that is deeply troubled. Armed pro-Russian separatists are battling security forces in the east of the country, Russia is threatening to switch off Ukraine's gas supplies for non-payments of debts, and Kiev must conduct painful economic reforms as a condition for Western aid.
Heavy fighting raged in eastern Ukraine on Wednesday for a third consecutive day, with casualties on both sides. The Ukrainian army pressed an offensive against the separatist stronghold of Slaviansk.
The White House said in a statement that Obama had approved an additional $23 million in defense security assistance to Ukraine since early March, including $5 million for "the provision of body armour, night vision goggles, and additional communications equipment".
Obama later delivered a keynote speech in Warsaw's Castle Square as part of celebrations to mark 25 years since it held its first partially-free election, shaking off decades of Soviet domination and Communist rule.
The U.S. leader drew parallels between Poland's achievements since then, including its strong economic growth and democratic system, and the prospects for Ukraine under its new leaders.
He also assured east European NATO allies which were once part of the Soviet Union or its Warsaw Pact military bloc that the United States would defend their territorial integrity.
"Poland will never stand alone. Estonia will never stand alone. Latvia will never stand alone. Lithuania will never stand alone. Romania will never stand alone," Obama declared.
Obama will fly to Brussels later in the day to meet leaders of the biggest industrialised nations for a Group of Seven summit from which Russian President Vladimir Putin, who had been due to host them in the Olympic city of Sochi, was excluded.
Putin is due to hold separate meetings with Germany's Angela Merkel, Britain's David Cameron and France's Francois Hollande on the sidelines of events in France this week commemorating the 70th anniversary of the World War Two D-Day landings.
Hollande has also invited Poroshenko to the ceremonies but there are no plans for him to meet Putin, diplomats said.
No Putin-Obama meeting is planned either but Obama said that if he encounters the Russian leader in France, he will urge him to rein in pro-Moscow separatists in eastern Ukraine or face further sanctions.
A French diplomatic source said Hollande would hold two separate dinners with Obama and Putin on Thursday evening, the former at a restaurant and the second at his Elysee presidential palace, to avoid the two guests crossing paths.
However, U.S. Secretary of State John Kerry will meet his Russian counterpart, Sergei Lavrov, in Paris on Thursday to discuss Ukraine and the conflict in Syria, Kerry's spokeswoman said.