The British government has told Ecuador it is "determined" to extradite WikiLeaks founder Julian Assange, who is seeking political asylum, and believes it can forcibly enter the Ecuadorian embassy in London.

A number of police officers gathered outside the Ecuadorian embassy, close to the Harrods store in Knightsbridge, on Wednesday night.

The dramatic development comes two months after Assange, an Australian, suddenly walked into the embassy in June in a bid to avoid being extradited to Sweden where he faces allegations of sexual assault.

Ecuador's minister for foreign affairs, Ricardo Patino, on Wednesday released details of a letter he said was delivered through a British embassy official in the capital of the South American country, Quito.

The letter said: "You need to be aware that there is a legal base in the UK, the Diplomatic and Consular Premises Act 1987, that would allow us to take actions in order to arrest Mr Assange in the current premises of the Embassy.