In information released to mark the annual World AIDS Day, the United Nations' World Health Organization (WHO) says Eastern Europe and Central Asia continue to show "dramatic growth" in the number of HIV infections.
WHO says new infections in the region have increased by 250 percent from 2001 to 2010.
And it said some 90 percent of the infections in the region occur in just two countries: Russia and Ukraine.
The UNAIDS organization, designed to bring UN agencies together to fight HIV transmission, said injecting drug use remains the leading cause of HIV infection in Eastern Europe and Central Asia -- although "considerable" transmission also occurs among the sexual partners of people who inject drugs.
The UNAIDS reports said that after slowing in the early 2000s, HIV incidence in Eastern Europe and Central Asia has been accelerating again since 2008.
It adds that unlike most other regions, AIDS-related deaths continue to rise in Eastern Europe and Central Asia.
The report has praise for Iran, saying HIV prevalence has "declined steadily" in the country since peaking in 2005 -- in part due to efforts by authorities to address health problems among injecting drug users.
The report says there is a network of more than 600 clinics that address drug injection, HIV and sexually transmitted infections in Iran, and that authorities have implemented programs to provide clean needles and opioid substitutes to injecting users. The report says an estimated 15 percent of people who inject drugs in Iran are living with HIV.
Worldwide, the UN says the number of new HIV infections fell to 2.7 million in 2010, down from 3.1 million in 2001. The UN says HIV/ AIDS have killed more than 25 million people over the past three decades. It says approximately 34 million people were living with HIV in 2010.
The Human Immunodeficiency Virus (HIV), at its most advanced stage of infection, becomes AIDS, or Acquired Immunodeficiency Syndrome.