Emmanuel Macron, France's president, center, listens as U.S. President Donald Trump, left, speaks at an arrival ceremony during a state visit on the South Lawn of the White House in Washington, D.C., April 24, 2018.

French President Emmanuel Macron has set out proposals to protect the European Union (EU) from foreign powers, cyber crime and political manipulation as populism continues to trouble the region ahead of Brexit and forthcoming European Parliament elections.

Publishing an open letter in European media outlets on Monday, Macron said that Europe was in danger and that Brexit, the U.K.'s departure from the EU due to take place on March 29, symbolized a "retreat into nationalism."

"Never since the second world war has Europe been so essential. Yet never has Europe been in such danger. Brexit stands as the symbol of that," he said Monday evening in a letter published in newspapers in all of the EU's 28 member states.

"Who told the British people the truth about their post-Brexit future? Who spoke to them about losing access to the EU market? … Retreating into nationalism offers nothing; it is rejection without an alternative. And this is the trap that threatens the whole of Europe," Macron added.

Macron said Europe was a "historic success" of reconciliation and a "project" that continued to protect its citizens but said there was a risk of complacency and what he called the "trap of the status quo."

"Europe, like peace, can never be taken for granted," Macron said, adding that "now is the time for a European renaissance" as he called on Europeans to resist "the temptation of isolation and division, I propose we build this renewal together around three ambitions: freedom, protection and progress."