US President Donald Trump said Thursday that the bond between America and its allies "forged in the heat of battle" of World War II was "unbreakable" as he spoke at a ceremony marking the 75th anniversary of the D-Day landings in northern France. "To all of our friends and partners, our cherished alliance was forged in the heat of battle, tested in the trials of war and proven in the blessings of peace. Our bond is unbreakable," Trump said. French President Emmanuel Macron on Thursday urged support for what he called the "alliance of the free world", as he marked the 75th anniversary of D-Day with Trump, who has frequently expressed skepticism over multilateralism. Trump spoke at a US cemetery in Colleville-sur-Mer in front of a beach codenamed Omaha during the landings which saw 150,000 Allied troops rush ashore in the world's biggest naval operation to liberate much of western Europe. "Those who fought here won a future for our nation, they won the survival of our civilization and they showed us the way to love, cherish and defend our way of life for many centuries to come," Trump said. He concluded: "May God bless our great veterans, may God bless our allies, may God bless the heroes of D-Day and may God bless America." Trump has caused the biggest crisis since World War II in the transAtlantic alliance after criticizing the NATO military alliance and openly criticizing European leaders, including his host on Thursday, Macron. The US leader began with a tribute to around 60 US veterans who were in the front row, many of them in wheelchairs. "You are among the very greatest Americans who will ever live. You are the pride of our nation. You are the glory of our republic and we thank you from the bottom of our hearts," he said. Macron, meanwhile, said, "We must never stop working for the alliance of the free world", citing as examples the UN, NATO and EU, multilateral organizations that Trump regularly criticizes. The ceremony was also a moment of great political symbolism, demonstrating unity at a time of tensions between the United States and Europe and in particular between Macron and Trump. Macron hailed D-Day as an example of how forces from Britain, Canada, the United States as well as the French resistance came together in the name of freedom. "We must prove ourselves worthy of this heritage of peace that we have been bequeathed," said Macron. He said being worthy of this "promise of Normandy" meant "never forgetting that free peoples can overcome all the challenges when they unite." Macron told Trump that modern France is "ready to work for this friendship between our nations which has brought so much to the history of mankind." Earlier, the leaders of France and Britain paid tribute to the sacrifice of D-Day veterans on Thursday, the 75th anniversary of the largest ever seaborne invasion that opened the way for western Europe's liberation from Nazi Germany. Inaugurating a memorial to the 22,000 soldiers under British command who were killed on June 6, 1944, and in the ensuing battle for Normandy, British Prime Minister Theresa May saluted the bravery of the soldiers, many of whom were still boys when they waded ashore under German fire. "It's almost impossible to grasp the raw courage it must have taken that day to leap from landing craft and into the surf despite the fury of battle," May told a small gathering that included Macron and veterans, their uniforms laden with medals. "These young men belonged to a very special generation ... whose incomparable spirit shaped our post-war world," she said. "They laid down their lives so that we might have a better life and build a better world." The Normandy landings were months in the planning and kept secret from Nazi Germany despite a huge trans-Atlantic mobilization of industry and manpower. Under the cover of darkness, thousands of Allied paratroopers jumped behind Germany's coastal defenses. Then, as day broke, warships pounded German positions before hundreds of landing craft disgorged the infantry troops under a barrage of machine-gun fire and artillery. Some veterans say the sea turned red with blood during the operation that would help turn the tide of World Two against Hitler. The devastation wrought by two world wars in the first half of the 20th century fostered a decades-long era of cooperation between European capitals determined to protect their hard-fought peace, giving rise to what is now the European Union. But even as Britain now tries sever its ties with the bloc, Macron said some ties between France and Britain were indestructible. "Nothing will ever take away the links of spilled blood and shared values. The debates of the present in no way take away from the past." An hour after sunrise, under clear blue skies, a lone piper atop the remnants of an artificial harbor played Highland Laddie to mark the hour the first British soldier set foot on French sand. The Mulberry harbor was constructed to enable the resupply of allied troops as they pushed the Germans back. Restored wartime jeeps and amphibious vehicles lined the beach at Arromanches and in villages along the Normandy shore the flags of Britain, Canada and the United States, the main contributors to the Allied force, fluttered in the breeze. Lines of white marble crosses on the clifftop above Omaha Beach today mark the resting place of more than 9,380 US soldiers who died during the military campaign. The commemorations come against the backdrop of two years of forthright diplomacy and "America First" policymaking by Trump and his administration that have shaken the NATO alliance and tested relations with erstwhile allies including Britain and France. On the eve of the anniversary, France's president evoked the spirit of D-Day, saying: "These allied forces that together freed us from the German yoke, and from tyranny, are the same ones that were able to build the existing multilateral structures after World War Two." "We must not repeat history, and remind ourselves what was built on the basis of the war." Commemoration events began in France on Wednesday. Khaki parachutes filled the skies above Sannerville as two British veterans in the mid-nineties joined several hundred paratroopers re-enacting the jumps behind enemy lines. Hundreds of British veterans crossed the English Channel on a specially chartered ferry.— Agencies