Europe's social and economic stability is being seriously threatened by the Aids epidemic, warn experts.
AIDS can be spread by sharing needles
Some 1.8 million people in Europe and Central Asia have HIV, according to the Joint UN Programme on HIV/Aids and the World Health Organization.
Both say the epidemic continues to spread unchecked and that European governments need to act now.
The European Union has a "prime opportunity" to work together to save thousands of people, the experts say.
Dr Jack Chow, WHO's assistant director-general, HIV/Aids, Tuberculosis and Malaria, said: "Building effective partnerships is key to make a significant and sustainable contribution towards proactively addressing the HIV/Aids epidemic in Europe.
"Countries of the newly enlarged European Union now have a prime opportunity to convert their commitment into concrete action and programmes against Aids."
He and colleagues will outline the scale of the problem at the European Ministerial conference on Aids, hosted by the Government of Lithuania and the European Commission, taking place on 16-17 September in Vilnius.
In Western Europe, deaths from Aids have declined due to the availability of HIV treatment.
But infection rates have continued to rise from 540,000 people living with HIV in Western Europe in 2001 to 580,000 by end 2003.
WHO and UNAIDS blame waning government commitments to prevention efforts and "complacency" linked to the availability of treatment.
In Eastern Europe and Central Asia, it is estimated about 15,000 people currently receive antiretroviral therapy out of 120,000 who need it.
The high cost of the drugs is a persistent barrier, say WHO and UNAIDS.
Lars O Kallings, special envoy of the UN Secretary-General for HIV/AIDS in Eastern Europe, said: "Given that 80% of those infected in Eastern Europe are young people, there is an urgent need for a massive and comprehensive response to reduce the vulnerability of young people and empower them to become active partners in the fight against Aids.
"If no action is taken, we will be faced with a larger Aids epidemic that risks crippling the region's social and economic development and undermining national security," he said.
Thomas Yocum from the Terrence Higgins Trust said: "The speed with which the HIV epidemic is growing in Eastern Europe and Central Asia is alarming, and it is essential that governments across the world continue to provide leadership and support in the fight against HIV.
"With the information and experience which already exists in helping to prevent HIV transmission, it would be a tragedy if we did not incorporate the things that we have already learned in other parts of the world which have been heavily impacted by the virus.
"Experience has shown us what we need to do - what we need now is the leadership to make it happen."