Russian customs authorities have seized a consignment of methadone bound for the UN's HIV prevention program in Tajikistan as contraband drugs due to a labeling misunderstanding, the UNDP said on December 18.

The mix-up happened earlier this month when the cargo of methadone -- which is used worldwide in HIV prevention programs around the world but is banned in Russia -- was seized at Moscow's Vnukovo airport while in transit from Germany.

Russia's customs service announced it had seized 5.8 billion rubles ($92.7 million) worth of methadone in a major swoop and the judicial authorities opened a criminal investigation into drug smuggling "on a large scale".

Meanwhile, the United Nations Development Programme (UNDP) said that the cargo had in fact been destined for battling the spread of HIV in Tajikistan. 

The UNDP said in a statement that the methadone represented “a life-saving treatment for people who inject drugs.”

“It was intercepted in Moscow after being wrongly labeled.  UNDP is in touch with authorities in Russia to resolve this matter and is available to answer their questions,” UNDP said in a statement issued in Dushanbe.

The Russian customs authorities said that the 2,000 vials of methadone, which are now in storage at Vnukovo, had not been declared by the transporter.

Methadone is an addictive opioid but is not taken via injection and is used in supervised programs for drug users to avoid injections and thus eliminate the risk of contracting the HIV virus from contaminated syringes.

Russia however bans methadone replacement therapy for drug addicts, in a hugely controversial stance due to the severity of the spread of HIV in the country since the fall of the Soviet Union.

According to UNAIDS, one million people were living with HIV in Russia in 2017 and HIV prevalence -- the percentage of people living with HIV -- among adults aged 15-49 years stood at 1.2 percent.