Julian Assange has given a clenched-fist salute as he welcomed a Swedish decision to drop a rape investigation against him as "an important victory".

But the WikiLeaks founder says his legal fight is not over and he cannot forgive the "terrible injustice" done to him across the last seven years of his life.

Appearing on a balcony of the Ecuadorian Embassy in London on Friday the 45-year-old told supporters and a large media throng he had been detained and slandered as his children grew up without him.

"That's not something I can forgive, it's not something I can forget."

The Australian has been holed up in the embassy since mid-2012 when he sought asylum there to avoid extradition to Sweden to face accusations he raped a woman in 2010 in Stockholm.