Story highlights Barack Obama and Vladimir Putin speak on the sidelines of a D-Day lunch

Russia's Putin and Ukraine's Petro Poroshenko shake hands, talk briefly

French President Hollande dined with Obama on Thursday before a separate dinner with Putin

Obama said he would reiterate comments on Ukraine if he and Putin met

A much anticipated encounter between President Barack Obama and his Russian counterpart, Vladimir Putin, came on the sidelines of a lunch held Friday to mark the 70th anniversary of D-Day

But a conversation between Putin and Ukrainian President-elect Petro Poroshenko may have been more fruitful.

"We believe it's a good thing they were able to speak, but it's not a substitute for the steps it (Russia) needs to take to deescalate things, especially violence," a senior administration official said. "It's a positive thing that they spoke, but more needs to be done."

The official said Putin has publicly voiced support for Poroshenko, but "he's not taking steps to back that up."

Putin and Poroshenko's conversation included plans to discuss a cease-fire in the coming days, the office of French President Francois Hollande said.

Photos: Photos: 70th anniversary of D-Day Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – World War II reenactors walk along Omaha Beach near Vierville-sur-Mer, France, on Friday, June 6, the 70th anniversary of D-Day. Hide Caption 1 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – British veteran John Trevor sits by the beach in Arromanches-les-Bains on June 6. Hide Caption 2 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – A British World War II veteran takes a picture of wreaths at the British War Cemetery in Bayeux, France. Hide Caption 3 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – World leaders pose for a photograph after ceremonies at Chateau de Benouville in Benouville, France. Hide Caption 4 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – World War II veterans from the U.S. 29th Infantry Division, from left, Hal Baumgarter, Steve Melnikoff, Don McCarthy and Morley Piper attend a D-Day commemoration on Omaha Beach. Hide Caption 5 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – Michel Colas talks with his grandsons Samuel Colas and Rafael Schneider at the Normandy American Cemetery in Colleville-sur-Mer, France. Hide Caption 6 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – Queen Elizabeth pays her respects after laying a wreath during a ceremony at the British War Cemetery in Bayeux, France. Hide Caption 7 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – A Dutch B-25 Mitchell, top, and Spitfire fly over Arromanches-les-Bains, France, during a joint French-Dutch ceremony. Hide Caption 8 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – British veteran James Rawe arrives at Sword Beach in Ouistreham, France. Hide Caption 9 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – The beaches of Normandy are seen from a helicopter on June 6. Hide Caption 10 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – French Republican Guards stay in the shade before a ceremony in Ouistreham. Hide Caption 11 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – President Obama and French President Francois Hollande survey Omaha Beach on June 6. Hide Caption 12 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – World War II veterans listen to President Barack Obama at the Normandy American Cemetery on June 6. Hide Caption 13 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – A Norwegian World War II veteran arrives for a joint French-Norwegian D-Day ceremony in Hermanville-sur-Mer, France. Hide Caption 14 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – President Obama greets veterans during the ceremony at the Normandy American Cemetery. Hide Caption 15 of 16 Photos: Photos: 70th anniversary of D-Day 70th anniversary of D-Day – From left, Australian Prime Minister Tony Abbott, Britain's Prince Charles and British Prime Minister David Cameron walk through Bayeux after the ceremony. Hide Caption 16 of 16

D-Day by the numbers

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"It would have to be mutual," the administration official said of the cease-fire. "Not just on the part of the people of Ukraine, but also the Russians."

During their informal aside, Obama told Putin that to reduce tensions in Ukraine, Russia must recognize Poroshenko as the country's legitimate leader and stop supporting separatists in eastern Ukraine.

Obama also told Putin that Russia must stop the flow of weapons across the border into Ukraine, Deputy National Security Adviser Ben Rhodes said.

Working with the Ukrainian leadership is the only way to reverse Russia's increasing isolation, Obama said, according to Rhodes.

"We didn't think it was the right time, place or circumstances to have a discussion," the senior administration official said. "We believe they haven't legitimately recognized Poroshenko."

The talk lasted 10 to 15 minutes.

Speculation had been brewing that the American and Russian leaders would meet, despite apparently elaborate steps taken by Hollande to avoid a tense encounter.

On Thursday, he dined with Obama before hosting a separate dinner with Putin.

The pair were also seated well apart for the D-Day lunch. With Hollande and the queens of Britain and Denmark between them, the two seemed unlikely to have to converse unless they wanted to.

The World War II commemorative events also brought Putin and Poroshenko together in their first face-to-face meeting.

They talked briefly before the leaders went to the D-Day lunch. German Chancellor Angela Merkel stood with them as they spoke.

Putin and Poroshenko shook hands before their informal exchange, Hollande's office told CNN.

No interaction was seen between Obama and Putin at that point.

'Lane of international law'

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Photos: Obama tours Europe Photos: Obama tours Europe Obama tours Europe – President Barack Obama and French President Francois Hollande pause for a moment of silence after laying a wreath at the Normandy American Cemetery in Colleville-sur-Mer, France, on Friday, June 6, the 70th anniversary of D-Day. Obama's travel agenda also includes Poland and Belgium. Hide Caption 1 of 14 Photos: Obama tours Europe Obama tours Europe – President Obama waves during a D-Day ceremony. Hide Caption 2 of 14 Photos: Obama tours Europe Obama tours Europe – President Obama greets veterans during the D-Day ceremony in Colleville-sur-Mer. Hide Caption 3 of 14 Photos: Obama tours Europe Obama tours Europe – President Obama laughs with British Prime Minister David Cameron, left, and Hollande during a G7 session in Brussels, Belgium, on Thursday, June 5. Hide Caption 4 of 14 Photos: Obama tours Europe Obama tours Europe – The G7 heads of state pose for a group photo with the presidents of the European Council and the European Commission during the second day of their meeting in Brussels on June 5. Hide Caption 5 of 14 Photos: Obama tours Europe Obama tours Europe – European Commission President Jose Manuel Barroso, left, and European Council President Herman Van Rompuy welcome Obama at the G7 meeting in Brussels on Wednesday, June 4. Hide Caption 6 of 14 Photos: Obama tours Europe Obama tours Europe – From left, Queen Mathilde and King Philippe of Belgium, Polish first lady Anna Komorowska, Obama and Polish President Bronislaw Komorowski attend a ceremony in Warsaw, Poland, on June 4 to mark the 25th anniversary of Poland's return to democracy. Hide Caption 7 of 14 Photos: Obama tours Europe Obama tours Europe – Obama speaks at the 25th anniversary celebrations in Warsaw on June 4. Poland's historic election, led by the Solidarity movement in 1989, "was the beginning of the end of communism -- in this country and across Europe," Obama said. Hide Caption 8 of 14 Photos: Obama tours Europe Obama tours Europe – Obama meets with Ukrainian President-elect Petro Poroshenko in Warsaw on June 4. Obama voiced his support for Poroshenko and called for the international community to "stand solidly behind" him as his government tries to quell a pro-Russian separatist uprising in the country's east. Hide Caption 9 of 14 Photos: Obama tours Europe Obama tours Europe – Obama and Komorowski gesture toward each other at a news conference in Warsaw on Tuesday, June 3. Hide Caption 10 of 14 Photos: Obama tours Europe Obama tours Europe – Obama, at right, is seated with a U.S. delegation as he participates in a bilateral meeting with Polish Prime Minister Donald Tusk and the Polish delegation in Warsaw on June 3. While in Poland, Obama announced he would ask Congress for $1 billion to be put toward bolstering NATO's security alliance in Europe. Hide Caption 11 of 14 Photos: Obama tours Europe Obama tours Europe – A Polish security official, right, stands watch as Obama and Komorowski make statements after meeting U.S. and Polish troops at an event in Warsaw on June 3. The main focus of Obama's Poland visit comes Wednesday, June 4, when he will give a speech 25 years after the nation's historic elections of 1989. Hide Caption 12 of 14 Photos: Obama tours Europe Obama tours Europe – Komorowski welcomes Obama at his residence in Warsaw on June 3. Obama hailed Poland as "one of our great friends and one of our strongest allies in the world." Hide Caption 13 of 14 Photos: Obama tours Europe Obama tours Europe – Obama waves from Air Force One before departing from Joint Base Andrews in Maryland on Monday, June 2. It's Obama's third foreign trip in as many months, and it caps a period of heavy foreign-policy focus for the President. Hide Caption 14 of 14

Speaking Thursday in Brussels, Belgium, Obama said he and Putin were likely to cross paths in France, although no formal meeting was planned.

Obama said then that if they spoke, he would give Putin the same message on Ukraine that he has given him in phone calls over past weeks and in his public statements.

Putin "has a chance to get back into a lane of international law," he said.

Obama said Putin could start by recognizing Poroshenko, stopping the flow of weapons over the border into Ukraine and ceasing Russian support for pro-Russian separatists in Ukraine.

Putin, in an interview with French television station TF1, did not discount the possibility of meeting with Obama.

"As for my relations with Barack Obama, I have no reason whatsoever to believe he is not willing to talk to the President of Russia," he said. "But ultimately, it is his choice. I am always ready for dialogue, and I think that dialogue is the best way to bridge any gaps."