Some 8,000 people with HIV in war-torn eastern Ukraine face a critical shortage of medicine and their supply will run out in mid-August unless a blockade is lifted, a UN AIDS envoy has warned.

Speaking ahead of the International AIDS Society conference, which opened in Vancouver, Canada, on Sunday, Michel Kazatchkine called on key nations to intervene as soon as possible.

"I am calling on the United States, Germany, France, Ukraine and Russia to do something," said Kazatchkine, the UN Secretary General's special envoy for AIDS in Eastern Europe and Central Asia.