With just weeks to go before the EU-wide vote, France’s struggling centrists are ramping up their anti-populist rhetoric in an effort to retake the lead in polls.
“Nationalism only leads to war,” Mrs Loiseau told a rally in the northern port city of Caen, quoting former French leader François Mitterrand.
The European Union is “both a legacy and a work-in-progress,” the ex-European affairs minister added.
“We must join forces to put a stop to this deadly and war-like nationalism and build a future of peace and prosperity in Europe.”
In an interview with Europe 1 radio later in the day, Mrs Loiseau lashed out at her far-right rival Marine Le Pen, saying that it would be “bad news for the French” if her Rassemblement national (RN) party won the most French seats in the EU parliament.
Her warning came after a poll on Sunday showed the RN winning 22 percent of the French vote, just ahead of Mr Macron’s La République en Marche (LREM).
The LREM party would obtain just 21.5 percent of the vote, the Ipsos poll of 1,500 people conducted on May 2-3 for France Television and Radio France showed.
On April 18-22, some 23 percent of the people polled said they would vote for Mr Macron’s LREM, against 22 percent for the RN.
Dissatisfaction over slow economic growth, ongoing threats to Europe by Islamist terrorist groups and a backlash against illegal immigration have boosted support for far-right populist parties across the bloc.
This has allowed the RN and other eurosceptic anti-immigration parties in other EU states to ride a wave of public anger, and call for a return of powers from Brussels to national capitals.
Last month, Mrs Le Pen promised her voters a “new European harmony” after announcing that her party would join a parliamentary group formed by Italy’s Deputy Prime Minister Matteo Salvini, who is also the leader of the far-right League party, after the election.
Mr Salvini expects the “European Alliance of Nations” bloc to become the largest in the EU parliament.
Outgoing far-right MEP Nicolas Bay, who is seeking re-election, shared Mr Salvini’s enthusiasm, saying in a joint interview with AFP and Le Figaro newspaper that the European Alliance of Nations group would be made up of “90 to 100” lawmakers.
Meanwhile, Mr Salvini has convened a big Milan meeting of anti-EU parties for May 18, which Mrs Le Pen is expected to attend.
Europe’s nationalists have good reason to be confident. A survey released by Germany’s Bild newspaper in early March showed that far-right parties are poised to double their seats in the EU election.
The poll of more than 9,500 people showed the far-right Europe of Nations and Freedom Group, which includes Mrs Le Pen’s RN, was likely to win 67 seats, up from 37 now.
Far-right parties came out top in three of the six countries surveyed – France, Italy and Poland.