French President Emmanuel Macron sought to reset relations with Poland in a visit on Monday, at a time when Britain's departure and an upsurge of nationalism are reshaping alliances and undermining confidence in the European Union.

Macron stressed the importance of deeper military integration among EU states – a message likely to appeal to Poland and other former communist satellites of the Soviet Union that are unnerved by Russia's assertiveness since it annexed Crimea from Ukraine in 2014, Reuters said.

"I'll be happy the day Polish people can tell each other: ‘The day I'm attacked, I know Europe can protect us'. Because that day, the sense of European belonging will be indestructible," Macron said during a joint press conference with Polish President Andrzej Duda.

Read alsoPoland not planning to join Normandy format – foreign minister

Macron, whose rapprochement with Russian President Vladimir Putin in recent months has caused concern in Poland and eastern Europe, sought to offer reassurance, saying: "France is neither pro-Russian nor anti-Russian; it is pro-European."

Nearly three months after sparking controversy by calling the American-led transatlantic NATO alliance "brain-dead", Macron declared that "European defense is not an alternative to NATO, it's an indispensable complement".

Relations between Poland and France soured in 2016 after Poland's nationalist Law and Justice (PiS) government scrapped a $3.4 billion helicopter deal with the European manufacturer Airbus, which France thought was largely agreed.

Since then, there have been clashes over issues ranging from climate change policy, where the PiS government remains firmly wedded to coal-fired power stations, and Poland's adherence to the rule of law – a bitter bone of contention with Brussels.

Macron, a fervent European integrationist, has decried nationalist governments such as Poland's and, along with the EU executive in Brussels, criticized efforts by PiS to bring courts and media under closer government control.

Duda said he hoped Macron's visit would mark a breakthrough in Franco-Polish relations and signaled Poland's readiness to take part in a project to create a European tank.

"Today France is definitely a power on a European scale, and France's role after Brexit will without doubt grow," he said.

Macron said he had had a frank discussion with Duda about reforms of Poland's justice system, and that he hoped Warsaw's dialogue with Brussels on the issue would "intensify."

Both countries want to keep generous funding for their agricultural sectors in the next EU budget, but Paris wants the bloc to take a bigger role in managing inward migration and on the climate, while Warsaw rejects EU policies on both matters.

Macron may, however, be keen to explore new alliances in Europe amid tensions with Germany over his ambitious EU reform plans, and said he wanted to hold a summit with Germany and Poland in the coming months.