(CNN) -- U.S. President Barack Obama paid tribute Friday to the U.S. servicemen who "defied every danger" to pour onto the beaches of Normandy 70 years ago in defense of liberty.
His remarks at the American Cemetery in Colleville-sur-Mer, which overlooks Omaha Beach where so many fell, are part of a series of solemn events to commemorate the D-Day landings in northern France.
Obama, who arrived flanked by French President Francois Hollande, shook hands with elderly veterans before the presentation of colors and playing of the two countries' national anthems.
Obama said he was honored to be there "to pay tribute to the men and women of a generation who defied every danger: among them, our veterans of D-Day."
Lengthy applause rang out as the U.S. President said he was humbled by the presence of some of those veterans at the ceremony.
"Here, we don't just commemorate victory, as proud of that victory as we are; we don't just honor sacrifice, as grateful as the world is; we come to remember why America and our allies gave so much for the survival of liberty at this moment of maximum peril," Obama said.
Their story should remain "seared into the memory of a future world," he said, describing Omaha as "democracy's beachhead."
He said, "It was here, on these shores, that the tide was turned in that common struggle for freedom.
"What more powerful manifestation of America's commitment to human freedom than the sight of wave after wave of young men boarding those boats to liberate people they'd never met?"
In his words, Hollande recalled how the calm beach below had become an "awful battlefield" on this day 70 years ago, the sea turning red with blood, and paid tribute to the courage of all those there.
He also thanked the United States and other Allied forces for their efforts to liberate Nazi-occupied France.
The poignant ceremony concluded with a 21-gun salute and the playing of taps, as well as an overflight by military jets.
Obama and Hollande then moved among the veterans and military officials, shaking hands and thanking them for their service.
The cemetery, which sits on a cliff overlooking Omaha Beach and the English Channel, contains the graves of 9,387 U.S. servicemen, most of whom lost their lives in the D-Day landings.
Omaha was the deadliest of the landing sites because German forces were able to fire from fortified positions on the cliffs above as the first waves of soldiers reached the shore.
An elaborate international ceremony will be held later on Sword Beach in Ouistreham.
Hollande is hosting a lunch for more than a dozen world leaders at a chateau beforehand.
The event will be attended by Obama as well as Russian President Vladimir Putin, UK Prime Minister David Cameron and German Chancellor Angela Merkel.
The run-up to the commemorations has been dominated by the current crisis in Ukraine, which has sparked the worst East-West tensions since the end of the Cold War.
The D-Day landings, in which mainly British, U.S. and Canadian troops invaded occupied France, were a turning point in World War II.
More than 156,000 troops crossed the English Channel during the D-Day invasion in on June 6, 1944. Nearly 10,000 Allied troops were killed or wounded.
Nicholas Soames, grandson of Britain's wartime leader Winston Churchill, told CNN it was "very touching" that so many people had come to take part in what will probably be the last commemoration of the D-Day landings on this scale, since those who survived are now in their 80s and 90s.
Britain's Queen Elizabeth II is also in France for the occasion -- the only living head of state who served in World War II, working as a mechanic and military truck driver in the Women's Auxiliary Territorial Service.
Earlier, Hollande spoke at a war memorial in the city of Caen, Normandy, at a ceremony to honor civilian victims, and paid tribute to all those killed in the conflict.
He recalled the "strength of heart and bravery" of those who helped to liberate France from Nazi Germany, as well as the many victims in Normandy -- more of them civilians than soldiers.
While the war may be long over in Normandy, Hollande said, "The war is still here in this tumultuous, uncertain and sometimes threatening world -- and in all wars it is civilians who pay a heavy price."
The Queen, Prince Philip and Prince Charles took part in a ceremony at the Bayeux War Cemetery, the largest of the Commonwealth cemeteries in France.
Canadian Prime Minister Stephen Harper was also in Normandy to honor the Canadian forces that stormed Juno Beach 70 years ago.
"It is a source of enormous national pride that Canadians played such a pivotal role in ensuring the success of the D-Day landings," he said in a statement.
"We are also deeply humbled by the enormous sacrifices made by our fellow citizens, who with grim determination, stood shoulder-to-shoulder with like-minded allies to fight evil."
A fireworks display was staged Thursday night along the Normandy coastline where the landings took place.
Putin was excluded from a meeting of G7 leaders held this week in Brussels, Belgium, as part of measures to sanction Moscow over its annexation in March of Ukraine's Crimea region.
While both Putin and Obama are attending the D-Day events, they have no scheduled meeting -- although the U.S. President has said it's likely their paths will cross.
Hollande dined separately with each of the two leaders Thursday evening.
The D-Day events may also bring Putin and Ukrainian President-elect Petro Poroshenko face to face.
Asked in an interview with French television station TF1 if he would speak with Ukraine's new leader, Putin said he will not "evade" Poroshenko or anyone else.
Poroshenko also did not exclude the possibility of a meeting.
At a news conference Thursday, Obama said the G7 nations were united in their support of Ukraine and urged Putin to take steps to deescalate the pro-Russian separatist unrest in the country's east.
Putin "has a chance to get back into a lane of international law," Obama said. But for this to happen, he said, Putin must take steps over the coming weeks that include engaging with Ukraine's new President, stopping the flow of weapons over the border into Ukraine and ceasing Russian support for pro-Russian separatists in Ukraine.
Poroshenko, who was elected last month, is due to be sworn in Saturday.
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