It said there were fears Mr Assange’s human rights might be violated.
Foreign minister Ricardo Patino accused the UK of making an “open threat” to enter its embassy to arrest him.
Mr Assange took refuge at the embassy in June to avoid extradition to Sweden, where he faces questioning over assault and rape claims, which he denies.
The Australian national said being granted political asylum by Ecuador was a “significant victory” and thanked staff in the Ecuadorian embassy in London.
CONTINUED at BBC News.