This spending, equivalent to 1.5% of the EU's gross domestic product, would allow Europe to mobilize some 300,000 soldiers to defend itself against Russia, the study by research institute Bruegel and the Kiel Institute for the World Economy said.

The study also called for closer coordination and joint procurement, noting that despite Europe's financial means, defence coordination within the continent remains a major challenge among national armed forces.

Most European states have come under increased pressure from U.S. President Donald Trump to ramp up military capabilities further, with his defence minister last week warning Europe against treating America like a "sucker" by making it responsible for its defence.

German Chancellor frontrunner Friedrich Merz on Thursday cast doubt on Washington's future presence in NATO while U.S. National Security Advisor Mike Waltz gave all NATO members a June deadline for fully meeting the defence spending target of 2% of GDP.

The Bruegel and Kiel study suggested increasing European defence spending to up to 4% of GDP per year, from the current 2%. Half of that could be financed by common European debt and used for joint procurement, while the rest could be covered nationally, the authors said.

The study noted that Moscow had significantly increased its military capacities since the Ukraine war, citing the mobilization of around 700,000 soldiers in Ukraine and a sharp increase in production of tanks and armoured vehicles.

It showed that for 50 additional brigades, Europe would need 1,400 new main battle tanks and 2,000 infantry fighting vehicles, a number that would exceed the current stocks of the entire German, French, Italian and British land forces.

"In economic terms, this is manageable ... That is far less than had to be mobilized to overcome the crisis during the COVID pandemic, for example," Guntram Wolff, co-author of the study, said in a statement.

($1 = 0.9556 euros)