Dmitry Medvedev, Russia’s president, on Wednesday broke a taboo on constitutional change when he asked parliament to extend the presidential term from four to six years, a move that could pave the way for Vladimir Putin to return as head of state for a further 12 years.

Mr Medvedev used his first annual state of the nation address since taking over from Mr Putin to deliver a threat to deploy missiles in Russia’s Baltic enclave of Kaliningrad in response to US plans to base a missile system in Poland and the Czech Republic.