Speaking just steps away from where 9,388 members of the US military who participated in the landings are buried, Mr.

Biden warned that democracies across the globe were once again under threat.

He added that autocrats were closely watching the Western response to Ukraine.

The president, born in 1942, will likely be the last US leader to have been alive at the time of the operation to liberate Nazi-occupied France.

A host of world leaders were present at ceremonies on Thursday, including French President Emmanuel Macron, King Charles III, and Canadian Prime Minister Justin Trudeau.

'Thank you to the Ukrainian people for their bravery.

We are here and we will not weaken,' Mr.

Macron said, as the gathered world leaders gave Ukrainian President Volodymyr Zelensky a standing ovation.

Russian President Vladimir Putin, who was not invited to Thursday's commemoration ceremony, launched a full-scale invasion of Ukraine in 2022.

Russia was a key ally during World War Two.

Its victory on the eastern front was fundamental, like the western front Allied assault that followed D-Day, in bringing Nazi Germany to its knees.

Throughout the speech, Mr.

Biden frequently drew connections between the fight against fascism in World War Two and the ongoing war in Ukraine.

Before a field dotted with the small, white tombstones of the dead US servicemembers, the president warned, 'the autocrats of the world are watching closely to see what happens in Ukraine.

' He vowed the US would 'not walk away' from the conflict, claiming 'if we do, Ukraine will be subjugated, and it will not end there.

Ukraine's neighbors will be threatened, all of Europe will be threatened.

' And he launched a direct attack on President Putin, referring to the long-term Russian leader as a 'tyrant.

'The president also sought to rally Western leaders, repeatedly highlighting the increasing threat from anti-democratic forces across the world and of freedom coming increasingly under threat.

He hailed the efforts of the 'noble band of brothers' who participated in the D-Day landings, saying 'the men who fought here were heroes.

They knew - beyond any doubt - there are things that are worth fighting and dying for.

Freedom is worth it.

Democracy is worth it.

America is worth it.

The world is worth it.

'Accompanied to the ceremony by President Macron, Mr.

Biden emphasized the importance of enduring partnerships between democracies across the world.

Emphasizing the value of the NATO alliance, Mr.

Biden said 'what the allies did here 80 years ago far surpassed anything we could have done on our own,' adding it was 'a lesson that I pray we Americans never forget.

' The comments come amid increasing isolationism in parts of the Republican Party.

Many members of the party have grown increasingly skeptical of sending military aid to Ukraine.

President Biden has blamed the party's delay in approving fresh aid for some of Ukraine's battlefield losses in recent months.

In an earlier interview with ABC News, Mr.

Biden defended his decision to allow Ukraine to use US weapons to strike directly on Russia.

He emphasized the strikes would be limited to areas around the border and would not extend to strikes on the capital, Moscow.

Present at the ceremony in the Normandy sunshine were a number of US soldiers who fought in the landings, which remain the largest seaborne invasion in history.

Several of the men, identified by baseball caps showing their service, were awarded the Legion d'Honneur - France's highest civilian honor - by Mr.

Macron.

Earlier in the day, Prime Minister Justin Trudeau took part in a separate ceremony commemorating the 381 Canadians who died on D-Day as they stormed Juno Beach.

Echoing Mr.

Biden's message, the Canadian leader said: 'We must all continue to stand for democracy day in day out, we owe it for future generations.

' The Prince of Wales, Prince William, was also present at the Canadian commemorative ceremony at Juno Beach in Normandy.

He thanked Canadian veterans for their 'extraordinary acts of bravery and sacrifice.

' At a British ceremony, King Charles III laid a wreath at the British Normandy Memorial in Ver-sur-Mer with a note attached touching on the sacrifices made on D-Day.

In a speech, he said that he hoped the sacrifice made by the D-Day veterans will 'never be made again.

'