One in seven people with HIV in Europe is unaware of their infection, the EU and World Health Organization reported Tuesday as 2015 marked another record year for new HIV cases in the region.

"HIV/AIDS continues to be a serious problem in Europe... The European Centre for Disease Prevention and Control's (ECDC) estimate that one in seven people living with HIV are unaware of their status is particularly worrying," EU Health Commissioner Vytenis Andriukaitis said in the report released ahead of World AIDS Day on Thursday.

"People who do not know they are infected cannot benefit from life-saving treatment, and can continue to transmit the virus to others," he noted.

The ECDC figure is based on data from the 28 EU nations plus Iceland, Liechtenstein and Norway.

Almost half of cases in those countries -- 47 percent -- are diagnosed at a late stage of infection, the ECDC said, estimating that on average it takes almost four years before an HIV infection is diagnosed and reported.

Sex between men remains the main reported HIV transmission mode in those 31 countries, accounting for 42 percent of diagnoses. Men who have sex with men is the only group that has seen a steady increase in infections over the years, the report said.

Heterosexual sex accounts for 32 percent of diagnoses, followed by drug use at four percent.

- High rates of infection -

Meanwhile, Europe registered its highest number of new HIV cases in a single year in 2015, at 153,407 cases, up from 142,000 in 2014, the WHO said.

The 2014 figures were also a record number, driven by cases in Russia and immigrants who acquired the virus after arrival.

The WHO regional office for Europe has a different definition of Europe and compiles data from 53 countries.

Almost 80 percent of the 2015 cases it tallied were reported in eastern Europe, 18 percent in western Europe and three percent in central Europe.

Russia, where HIV remains a largely taboo subject, accounted for 64 percent of all newly diagnosed infections in the WHO's European region, and 81 percent of cases in eastern Europe.

There, heterosexual sex is the main route of transmission of the virus which is spread through contact with contaminated body fluids.

Other countries with high rates of new infections last year were Ukraine, Belarus, Estonia, Moldova, Latvia and Georgia.

"Despite significant efforts, HIV remains among the main public health concerns in the WHO European region, in particular in its eastern part," the WHO regional director for Europe, Zsuzsanna Jakab, said.

She urged member countries to implement a new action plan they endorsed in September, including improving access to HIV testing and prevention methods, to reverse the HIV epidemic.