The Finnish foreign minister handed the accession document to the US secretary of state who declared Finland a member. Finland shares a 1,340-km (832-mile) eastern frontier with Russia and after the war in Ukraine began Helsinki chose the protection of Nato's Article Five, which says an attack on one member is an attack on all. Mr Peskov told the BBC that Russia would be watching closely how Nato used Finnish territory "in terms of basing weapons systems and infrastructure there which will be right up close to our borders, potentially threatening us"