Finland is prepared to close all its border crossings with Russia if necessary and has warned that Moscow could try to smuggle soldiers or war criminals into the EU among the migrants it is deliberately sending across the frontier.

Elina Valtonen, Finland’s foreign minister, told the Financial Times that if Russia intensified its operation of allowing migrants from countries such as Yemen, Iraq and Syria to cross without documents, her country could restrict the filing of asylum applications to Helsinki airport — and so exclude its checkpoints along the land border.

Finland says Russia is using the migrants to put a kind of pressure on Helsinki that falls short of outright hostilities, a method sometimes known as “hybrid” warfare or operations.