Julian Assange — the founder of WikiLeaks who sought refuge in the Ecuadorean Embassy in London in 2012 to avoid extradition to Sweden — has been arbitrarily detained in violation of international law, a United Nations human rights panel has concluded.

The panel, the Working Group on Arbitrary Detention, will announce its decision on Friday morning in Geneva, according to officials there. Its findings are a symbolic victory for Mr. Assange, but they are not legally binding and may have limited, if any, practical significance.

Swedish prosecutors want to question Mr. Assange, an Australian citizen, over a rape accusation. Mr. Assange and his team of lawyers say that criminal inquiry is a pretext for prosecution, and that Mr. Assange is essentially a political prisoner, targeted by the United States and its allies because of WikiLeaks’ role in publishing more than 250,000 leaked State Department diplomatic cables — a deep embarrassment for the Obama administration — starting in 2010.

In a statement that WikiLeaks posted to Twitter on Thursday morning, Mr. Assange promised to leave the embassy at noon on Friday if the United Nations panel ruled against him. “However, should I prevail and the state parties be found to have acted unlawfully, I expect the immediate return of my passport and the termination of further attempts to arrest me,” the statement said.