(Updated) An unconfirmed number of the world's leading HIV/AIDS researchers and activists were among the 298 people killed on a Malaysian passenger jet that was shot down over Ukraine, although the airline has not yet released names and figures.

The researchers were en route to the 20th International AIDS Conference in Melbourne, Australia, set to begin Sunday.

The Sydney Morning Herald said those attending a preconference meeting in Sydney were told that around 100 of their colleagues were on the plane. Subsequent media outlets have since noted that the number may be fewer.

The plane, which was flying from Amsterdam to Kuala Lumpur, Malaysia, crashed yesterday. American intelligence authorities believe a surface-to-air missile brought the aircraft down in eastern Ukraine but it is not yet clear who fired it.

"There's been confirmed a number of senior people who were coming out here who were researchers, who were medical scientists, doctors, people who've been to the forefront of dealing with AIDS across the world," Victoria Premier Denis Napthine told reporters in Melbourne. "The exact number is not yet known, but there is no doubt it's a substantial number."

The former president of the International AIDS Society Joep Lange, MD, a well-known HIV researcher from the Netherlands, was believed to be among the dead, along with his wife and collaborator Jacqueline van Tongeren.

Dr. Joep Lange. JEAN AYISSI/AFP/Getty Images

Chris Beyrer, president-elect of the International AIDS Society, said if reports of Dr. Lange's death were true, "then the HIV/AIDS movement has truly lost a giant," the Associated Press reported.

Nobel laureate Dr. Francoise Barre-Sinoussi, codiscoverer of the AIDS virus and president of the International AIDS Society, paid tribute to Dr. Lange in a speech in the Australian capital, Canberra.

"Joep was a wonderful person — a great professional — but more than that, a wonderful human being," she said. "If it is confirmed, it will be a terrible loss for all of us. I have no words, really, to try to express my sadness. I feel totally devastated."

The conference will continue out of respect for the lives lost: "Because we know that it's really what they would like us to do," she told reporters.

Dr. Lange had been working on HIV since the earliest years of the epidemic, participating in clinical trials and research across the world, Dr. Barre-Sinoussi said.

"The cure for AIDS may have been on that plane. We just don't know. You can't just help but wonder about the kind of expertise on that plane," Trevor Stratton, an HIV consultant, told an Australian television station.

The conference is expected to be attended by 14,000 delegates from around the world. Former US President Bill Clinton and British activist/musician Sir Bob Geldof are to deliver speeches.

The World Health Organization's Geneva-based spokesman Glenn Thomas, who was en route to the conference, was also among the dead, said Christian Lindmeier, spokesman for the organization's Western Pacific region. "Everybody's devastated," Lindmeier said. "It's a real blow."

Some 35 million people live with HIV, although global AIDS-related deaths and new infections have fallen by more than a third in a decade, raising hopes of beating the killer disease by 2030, the United Nations said Wednesday.

This story has been updated to note that the number of conference attendees traveling on the flight has not yet been confirmed.