* Hollande to discuss Ukraine separately with US, Russian leaders
* Paris in lockdown as British Queen also arrives
* Hollande working to get Putin, Ukrainian leader to meet on D-Day
(Adds Hollande comments from G7 meeting in Brussels)
PARIS, June 5 (Reuters) - Criticised at home for a lack of initiative on Ukraine, French President Francois Hollande will hold separate dinners on Thursday with the U.S. and Russian leaders in an attempt to unlock Europe's worst security crisis since the Cold War.
His aim is to orchestrate an ice-breaking first meeting between Russian President Vladimir Putin and Ukrainian president-elect Petro Poroshenko on French soil, diplomats said, despite continued fighting in eastern Ukraine between government forces and pro-Russian separatists.
French officials have gone to elaborate lengths to keep U.S. President Barack Obama and Putin apart in Paris, at Washington's request, before Friday's 70th anniversary commemorations of the allied D-Day landings in World War Two, which will see 18 world leaders descend on the Normandy beaches.
The French capital goes into security lockdown from mid-afternoon when Obama and Putin fly in, while Britain's Queen Elizabeth arrives by train from London to begin a three-day state visit, her fifth since taking the throne in 1953.
"This is an important occasion to express gratitude and fraternity, but it is also major international event which should serve the interests of peace," Hollande told a news conference after a summit of Group of Seven (G7) leaders in Brussels - a meeting to which Putin was pointedly not invited.
Asked if a Putin-Poroshenko meeting in France was possible, Hollande replied: "Yes...I invited (Poroshenko) so he could be there, because he represents the Ukrainian people who suffered a lot during World War Two. He will be there alongside President Putin. President Putin was informed of that."
Putin said in French media interviews on Wednesday that he was open to meetings with both Poroshenko and Obama in France. While the U.S. leader has so far not taken him up on the opportunity, the two countries' foreign ministers will meet on Thursday.
Underscoring the sensitivities, Hollande will rush from meeting the Queen at his Elysee Palace to a chic restaurant overlooking the Champs-Elysees avenue to dine with Obama before going back to his residence for a late supper with Putin.
Hollande has spent much of the week, first in Poland and then in Brussels, trying to create a diplomatic opening on Ukraine after sending Poroshenko a last-minute invitation to the D-Day ceremonies. Ukrainians fought in the Soviet Red Army that defeated Nazi Germany.
French diplomats say Hollande, who met Poroshenko in Poland on Wednesday, wants at the very least to get Putin and the Ukrainian to shake hands at a closed-door lunch of leaders on Friday at the 18th-century Chateau de Benouville, where rooms are ready for bilateral meetings.
This, they say, would be a tacit acknowledgement that the Russian leader recognises Poroshenko's legitimacy, the day before he is sworn in, opening the door for dialogue.
In an apparent signal of recognition, Russia's deputy foreign minister, Grigory Karasin, said Moscow's ambassador to Ukraine would attend Poroshenko's inauguration.
"All these leaders with the Ukrainian president is extremely symbolic, even if it is not a political event," said Camille Grand, director of the Paris-based Foundation for Strategic Research. "Poroshenko is not incompatible with Putin."
Interviewed by French media on Wednesday, Putin did not rule out a first encounter with a pro-Western Ukrainian leader since Moscow's annexation of Ukraine's Crimea region in March.
"You know, I don't plan to evade anyone," Putin told TF1 television when asked if he was willing to meet Poroshenko. "There will be other guests, and I'm not going to avoid any of them. I will talk with all of them."
His relations with Ukraine as well as with the European Union and the United States have been strained since pro-western protesters pushed a Moscow-friendly Ukrainian president from power in February and Russia then seized and annexed Crimea.
Moscow has deployed tens of thousands of troops near the Ukrainian border and warned it could send them in to protect Russian-speakers. Poroshenko and Ukraine's pro-Western government have ignored Moscow's demands for an end to Kiev's military operation against the separatists.
Whether he is made to feel unwelcome or not, Putin has the chance to show his defiance over Ukraine at his first encounter with Western leaders since Crimea.
He will meet British Prime Minister David Cameron before his dinner with Hollande and will sit down with German Chancellor Angela Merkel, Moscow's biggest European trade partner, before Friday's D-Day commemoration.
For Hollande, the Obama dinner will also be the opportunity to raise concerns about a possible $10 billion-plus U.S. fine on BNP Paribas that he considers "disproportionate".
(Additional reporting by Julien Ponthus in Brussels; Editing by Paul Taylor and Will Waterman)