The head of Nato declared that Finland and Sweden would increase Europe’s security as the two Nordic countries formally submitted their applications to join the transatlantic defence alliance.

“This is a good day at a critical moment for our security,” Jens Stoltenberg said on Wednesday as the Finish and Swedish ambassadors handed in their requests at a ceremony at Nato’s headquarters in Brussels. He added: “You are our closest partners and your membership in Nato would increase our shared security.”

The momentous decision by Helsinki and Stockholm to pursue membership of the alliance comes after Vladimir Putin’s brutal invasion of Ukraine, a non-Nato member that shares a border with Russia, upturned decades of security thinking in the two Nordic countries.