WikiLeaks will release one million documents next year affecting every country in the world, founder Julian Assange said in a speech from the balcony of the Ecuadorian embassy in London on Thursday.

In a "Christmas message" marking six months since he sought asylum in the embassy to avoid extradition to Sweden over claims of rape and sexual assault, Assange also said the door was open to negotiations.

Assange said to cheers from around 100 supporters that despite spending half of 2012 holed up in the building it had been a "huge year" in which his anti-secrecy website had released documents about Syria and other topics.