The United Nations has warned that the new states of Central Asia are fast becoming one of the main new routes for opium and heroin, produced in Afghanistan, and bound for Russia and Europe.

The BBC's Louise Hidalgo: "These lands are becoming a trade route once again, but now it's moving a far more deadly cargo"

Afghanistan is now the world's biggest producer of illicit opium - the drug from which heroin and morphine come. And the UN drugs control agency estimates that up to 60% of the crop destined for export is now being trafficked through the mountains and deserts of the former Soviet states.

The two main frontline states are Tajikistan and Turkmenistan. Between them, they share more than 1,500km of border with Afghanistan - crossing some of the highest mountains and most inhospitable desert on earth.

And it's a border that - in the collapse that has followed the end of the Soviet Union - has become increasingly difficult to control.

Border guards seize a suspected drugs smuggler

Almost weekly in Tajikistan there are shoot-outs between smugglers and the Russian border troops who still patrol the Tajik frontier. While in Turkmenistan, perhaps the most secretive of all the Central Asian states, officials struggle to fight this growing trade, with limited resources and - until now - little outside help.

The Turkmen town of Kushka was the southernmost point of the Soviet Union, and is one of the only places where Central Asia's border with Afghanistan is officially open.

The Soviets opened the bridge there during their ill-fated Afghan campaign. And now it is a busy trading route. Every day more than 100 trucks pass across the narrow bridge that marks the frontier - bringing oil and gas and wheat.

But some are carrying a more deadly cargo too. In the past three years, 70 tonnes of opium and heroin and other drugs have been seized by the Turkmens at Kushka.

Kushka guards search a truck for drugs

But customs chief Sergei Markeylov says, with few resources to fight the new trade, it is a difficult battle.

"We have one X-ray machine that works; the other stopped working a year and a half ago. So we have to search by hand. And that's sometimes difficult, particularly when the containers are closed. We know, that if we're going to make more precise and effective searches, we have to have modern equipment."

There is no telephone or radio to contact police checkpoints further up the road, if trouble breaks out. Some border officials even complain of no fuel for their cars.

The old wire fence that runs along the border is in places broken, and anyway provides little challenge for the smugglers.

Officials fight the drug trade with limited resources

Drug experts say by comparison that they are increasingly well-armed. Rocket launchers have been seized in skirmishes. And some even have night-vision - equipment the Turkmens can only dream of.

Bogdan Lisovich, the UN drug control agency's representative in Central Asia, says it is time the rest of the world took note.

"Afghanistan now produces 75% of the world's illicit opiates. This year's crop is the largest ever recorded in any crop - three times the amount produced in the rest of the world combined.

"And that's a serious threat for the security of Central Asia, with its permeable borders and poor infrastructure."

Addiction on the rise

The multi-billion dollar trade is already making its impact felt in countries like Tajikistan, feeding on the lawlessness that has followed nearly five years of civil war.

The BBC's Louise Hidalgo on a uncertain future for the people of Temirtau

And increasingly the countries of Central Asia are facing their own internal problem of drug addiction too.

The town of Temirtau in central Kazakhstan lies more than 1,000km away, across the Kazakh steppe, from the Afghan border.

The town is home to what was the largest steel plant in the former Soviet Union, where the Kazakh president himself rose through the party ranks from the shop floor.

The steel plant is one of the few functioning factories in Temirtau

The steel plant is still working, under new private owners. But the other factories in the town are not, and in the years that have followed the collapse of the Soviet Union, thousands have lost their jobs.

Increasingly it is to drugs that the young and out-of-work have turned. Aid agencies now estimate that one in 10 people under the age of 30 in Temirtau inject opium or heroin. One girl we met, Kisenya, started at the age of 12.

Aids threat

The drugs epidemic has brought a new nightmare too. Temirtau registered its first case of HIV in 1996.

Now - officially there are more than 800 people with HIV; the true figure may be three times that - in a town of 160,000. And Temirtau has the highest rate of Aids in all of Kazakhstan.

Opium addict Sveta: "The only way I'll ever stop is to leave"

Sveta lives with her nine-year-old daughter in a flat where there is no electricity or gas, and water only occasionally. She has not had a job in years, and what money comes in goes on drugs.

When she can get it, she'll inject two grammes of opium a day on average - at a dollar a shot. She says for her there is only one way out.

"This is a sick town, I know that. There are too many people here for whom drugs has become their life.