The tragic loss of delegates killed on the way to an AIDS conference in Melbourne should be used to push the life-saving agenda of the meeting, the UN AIDS chief says.

The 20th International AIDS Conference was nearly cancelled after it emerged many of the 298 who died when Flight MH17 crashed in Ukraine were delegates and their family members.

The former president of the International AIDS Society (IAS) and "giant" of HIV research, Joep Lange, was on board.

Organisers still don't know how many of the 12,000 researchers coming to Melbourne for the five-day conference were aboard MH17.

Media reports put the number at 108, but a spokesman for the International Aids Society said there had been no confirmation of that figure.