Finland has become the 31st member of the Nato security alliance

Finland has become the 31st member of the Nato security alliance, doubling the length of member states' borders with Russia.

The Finnish foreign minister handed the accession document to the US secretary of state who declared Finland a member.

Then in bright sunshine in front of Nato's gleaming new headquarters, Finland's white-and-blue flag joined a circle of 30 other flags.

Finland's accession is a setback for Russia's Vladimir Putin.