Supporters gathered in the street below, some of them carrying candles, the BBC reported.
Assange, a 41-year-old Australian, has been living in the embassy for six months. He sought asylum there to avoid extradition to Sweden where he is under investigation for alleged sexual crimes.
While no charges have been brought, the United States could prosecute Assange for publishing leaked diplomatic cables. He said Thursday the U.S. Defense Department has called WikiLeaks' survival "an ongoing crime."
"While that remains the case and while my government will not defend the journalism and publishing of WikiLeaks, I must remain here," Assange said. "However, the door is open, and the door has always been open, for anyone who wishes to use standard procedures to speak to me or guarantee my safe passage."
Assange promised WikiLeaks will publish "millions of pages" in 2013 involving every country in the world. He described 2012 as a "huge year" for WikiLeaks.
The leaked diplomatic cables, allegedly supplied by Bradley Manning, a U.S. soldier, helped inspire the Arab Spring revolts. They included information on the lavish lifestyle of Tunisian President Zine el-Abidine Ben Ali and his family that fueled large protests there.