Africa once had 400,000 HIV-infected people. It now has nearly four million.

UN statement

Three UN agencies said that immediate action was needed to stem the rising number of cases of HIV, the virus that can lead to Aids.

Latest research suggests the number of people infected with HIV in eastern Europe and the former Soviet Union has jumped to 700,000, a rise of almost 75% in the space of a year.

Experts think the actual total could be up to five times greater.

The worst affected countries are Russia, Ukraine, Belarus, Moldova and Kazakhstan.

'Act now'

So far the virus has spread in the region mainly through the sharing of needles by intravenous drug users.

But specialists are warning that a new wave of infections through sexual contact could cause a massive rise in cases in the next three to four years.

Harm reduction: Ukrainian poster shows how to sterilise needles

The call for action was launched by the childrens' fund Unicef, the World Health Organisation and UN-Aids to coincide with a conference on Aids in Europe in the Danish capital Copenhagen.

They compared the situation to that in Africa before the epidemic.

"Africa once had 400,000 HIV-infected people," the statement said.

"It now has nearly four million. Our window of opportunity is not yet closed. We must act now."

'Failure to respond'

Experts at the conference suggested immediate practical steps such as needle exchange for drug users, treatment of sexually transmitted diseases at general practitioner level and condom promotion campaigns.

But French-based medical aid group Medecins Sans Frontieres said that it was shocked by the failure, in particular of the European Union, to respond to the problem.

"Today 500,000 young Russians are HIV positive. In 2005 10 million young people will be infected in Russia," a spokesman for the group said.

The epidemic could pose a serious economic and security threat, he added.

And it would have consequences for western Europe as well, with human traffickers bringing the virus across borders illicitly.