The UN's AIDS envoy for eastern Europe voiced fears Thursday for injecting drug users in Crimea who risk being cut off from a lifeline treatment prohibited in Russia.

Michel Kazatchkine said he was worried that heroin replacement programmes called opioid substitution therapy (OST) would end for these individuals, stripping them of a major benefit in the fight against HIV.

"I am obviously concerned for the risk that an abrupt cessation of access to OST would represent for the many people who have benefited from these programmes," Kazatchkine, the UN's HIV/AIDS envoy for eastern Europe and central Asia, told AFP by telephone from Geneva.

"OST is illegal in the Russian Federation. There is no OST whatsoever. With Crimea becoming a part of the Russian Federation, I don't see how OST programmes can be continued there."

The International HIV/AIDS Alliance, an NGO working to halt HIV spread, said more than 14,000 injecting drug users in Crimea risk being cut off from medicine and other services.

Most immediately at risk are about 800 Crimeans who depend on OST -- synthetic drug substitutes which are safer than the heroin they replace and are administered under medical supervision, curbing HIV infection by preventing needle-sharing.

"Current stocks of methadone and buprenorphine on the Crimean peninsula will only last for another few weeks at most," the alliance said.

"With the blocking of highways that connect Crimea to the mainland, getting medical supplies through is challenging and there are concerns that a major public health crisis will arise as a result."

- HIV risk if therapy cut -

AIDS experts say an oppressive approach to drug users often backfires. If they are stigmatised or jailed, they become more at risk of contracting HIV among themselves and transmitting it to others.

Once treatment is cut off, OST recipients will go into withdrawal and many are likely to revert to their old, unsafe drug habits, the British-based group explained.

Desperate for a quick fix, many will fall into the hands of unscrupulous drug dealers, revert to petty crime or prostitution to get money to buy drugs, and start sharing contaminated needles.

Contrary to Ukraine, where drug addicts have access to HIV prevention services like needle exchanges, condom distribution and HIV-testing, Russia takes a punitive approach to drug use that the alliance claimed was responsible for one of the highest rates of new HIV infections in the world.

"Injecting drug users represent nearly 80 percent of all HIV cases in the country," said the statement.

OST has been available in Crimea for almost a decade under the political control of Ukraine, which saw the number of new HIV cases among people who inject drugs drop from 7,127 in 2006 to 5,847 last year.

Andriy Klepikov, executive director of the alliance's Ukraine branch, urged Crimean authorities to "step in and ensure that critical supply chains are not disrupted and lives not put at risk as a result of territorial politicking".

Eastern Europe and Central Asia are considered black spots in the global HIV/AIDS pandemic, driven by intravenous drug use.

New infections in this region increased by nine percent in 2012 compared to 2011, the European Centre for Disease Prevention and Control (ECDC) said last November. Of the 102,000 new cases, three-quarters occurred in Russia.

The World Health Organisation (WHO), meanwhile, warned the political crisis also threatened efforts to fight tuberculosis in one of the world's hardest-hit countries.

Health services are usually the first to suffer when crisis-hit countries start shifting money to their defence budget, said Mario Raviglione, head of the WHO's anti-TB programme told reporters.

"One can expect that if this situation is prolonged and there is a conflict going on, ... that the TB situation would deteriorate," he told reporters.

In 2012, there were close to 41,000 newly discovered cases of TB in Ukraine, up from just over 34,000 the previous year, though health officials note the rise is partly due to better detection.