Anti-apartheid icon Nelson Mandela has entered the seventh day of a hospital stay for a lung infection as questions grow about where he is receiving treatment.

The 94-year-old patriarch of South Africa's democracy has been hospitalised since Saturday, first undergoing tests and later being diagnosed with the ailment.

Government officials avoided questions on Friday over where Mandela was receiving treatment. The nation's defence minister told journalists on Monday that Mandela was being treated at a Military Hospital near the capital, Pretoria. However, after local media reported Mandela wasn't there on Thursday night, a presidential spokesman refused to say where Mandela is being treated.

Mandela is revered for being a leader of the struggle against racist white rule in South Africa. He served one five-year term as president before retiring from public life.