Antonio Maria Costa, head of the UN Office on Drugs and Crime, has been visiting the country to assess the situation, touring north and western Afghanistan before meeting President Karzai and other leaders in Kabul.
BBC Afghanistan correspondent Andrew North has been travelling with Mr Costa. This is his diary from the trip.
29 May, Sher Khan Port, Afghanistan-Tajikistan Border
The UN is worried by a big rise in the opium trade
A low key arrival for the UN's drugs control chief: at one of Afghanistan's more remote frontier posts, on a small and battered motor boat.
Here, the Afghan border means the muddy waters of the Amu-Darya river.
In Tajikistan, Antonio Maria Costa has been looking at the impact of the Afghan drugs trade there.
Increasing quantities of opium and heroin from Afghanistan's poppy fields are being smuggled through the country - and other states along its northern border - en route to Russia and Europe.
"Welcome to Afghanistan," says the Kunduz provincial governor, as Antonio Maria Costa steps onto the river bank.
No concrete quayside here. Much of the port is still a war-shattered ruin.
"Nice to be here," Mr Costa responds. But the pleasantries don't last long.
The green tea is still being poured as he tells his hosts bluntly that efforts to curb Afghan drugs are failing.
"Not only has there been no success, the situation has deteriorated year by year since 2001."
Costa does not bring warm greetings from the neighbours either. "They're mad at you up in Tajikistan, I can tell you," he says with an ironic smile.
"The authorities there tell me they've seized six tonnes of heroin and opium on the border so far this year."
But his expressive Italian manner seems to go down well with his main host, General Daud, the commander of the militia force known as the 6th Corps and the real power in this region.
He's got a few gripes of his own. Among them are the past policies of the British government, which is leading international efforts to combat Afghan drugs.
Initially, it tried offering farmers money to destroy their poppy crops.
But as word spread, Daud says, many grew it deliberately, expecting the British cash. When it did not come, they harvested the opium.
"So it made things far worse."
This year there is widespread confusion about Afghan government policy, the general argues.
It has decreed that 25% of the poppy crop should be eradicated or cut down. But many farmers have interpreted that to mean the other 75% is legal, he says.
Costa's eyebrows rise.
29 May Kunduz Province
After lunch, there is another illustration of the scale of the challenge, with a visit to a poppy field.
It looks like any other, except there was no poppy-growing here last year.
Nor was there much elsewhere in the rest of Kunduz province.
But all that's changing. Even in traditionally low-producing areas, farmers are sowing the crop, anxious not be left out.
Farmers say they are confused by government policy The 78-year-old farmer is found in the huts nearby.
"Yes, it's the first time I've grown it," he admits reluctantly.
"But why this year?" demands his Italian visitor.
"Well everyone else is doing it, so why shouldn't I?"
Laughter from the crowd of officials and soldiers looking on.
"But don't you know this is against Islam?" says Mr Costa, holding up a poppy bulb.
The farmer looks up plaintively. "There's freedom now, it's a democracy isn't it?"
The crowd roars.
"No, I understand, you make more money," Mr Costa counters.
"If I rob a bank, I make more money, but it's against the law. "I'll come back next year and I want to see you in good shape and without poppy, okay."
There's a pause, then the farmer says: "Okay, next year, I will only grow it with your permission."
There is another explosion of laughter from the officials and soldiers, many of them chewing on opium seeds from poppy bulbs they have broken open.
30 May Kunduz City
The UN's drugs chief shares views, and lunch, with the governor of Kunduz We're at the government meeting hall, inside General Daud's spacious compound.
It's the first of several such meetings Mr Costa is having with militia commanders, governors and police chiefs during his visit.
This time, it's everyone from the four north-eastern provinces, including Badakshan, one of the main drug-producing areas.
Mirwais Yassini, head of Afghanistan's Counter-Narcotics Directorate is here, together with the British ambassador, Rosalind Marsden, and UK drugs officials.
Mr Costa takes a softer approach as he starts his speech, paying tribute to Afghans' struggle against the Soviet invasion and the Taleban.
"It's because of valiant fighters like you that I believe we are going to succeed in winning this domestic war against narcotics."
But the hopeful message doesn't last.
"Let's be frank, efforts to eradicate the poppy crop this year have failed."
It is not exactly a meeting of minds. While the general promises full co-operation in the fight against drugs, many of the other officials around the table use their speaking time for explanations, rather than ideas on dealing with the problem.
And what about the West doing more to reduce its demand for drugs, they ask.
Both the British ambassador and Mr Costa emphasise the fact that the opium poppy is regarded as against Islam, and that it is officially illegal in Afghanistan.
Yet one senior religious scholar admits that in many poppy-producing areas his counterparts often say that producing opium is "halal" or permitted in Islam, as long as it is sent to infidels abroad.
31 May Mazar-E Sharif
A short plane ride from Kunduz takes Mr Costa and his small team to the shrine city of Mazar-e Sharif and straight into another meeting with more governors, military chiefs and police commanders.
It seems this group of officials are more willing to be frank with the UN drugs chief about the problem, but only once they've made sure journalists are out of the room.
Their chief concern, we learn later, is the continuing power of the commanders, the militia chiefs who wield the real power in much of Afghanistan.
Under a nationwide scheme, they are supposed to be disarming.
But the message Antonio Maria Costa receives is that it is only when this happens that anything can be done about the drugs trade.
No one is naming names, but some commanders in this region are accused of being directly involved.
Others may be profiting from drugs by levying taxes on drugs cargoes passing through their areas.
And the underpaid police are easily corrupted and too under-resourced to fight back. The UN hammers out the drug issue with the British embassy
The UN drugs chief asks if the British military are helping fill the gap, when he visits the so-called Provincial Reconstruction Team they are running in the city.
They will pass on information about drugs trafficking if they come across it, but otherwise no is the answer from the commander.
It seems a contradiction, given the UK's lead role in fighting drugs.
But Colonel Duncan Francis says with the small number of troops he has at the PRT, he can only achieve his aims of boosting peace and security in the region - "peace support" as he calls it - if he has the "consent" of local people.
That means avoiding conflict "with criminal elements" and making his lightly-armed patrols a potential target.
This passive approach reflects the wider policy of the US-led coalition forces in Afghanistan right now, but many are calling for a re-think.
Because all the signs are that the drugs threat is rising.
In this province - Balkh - large amounts of opium and processed heroin are being trafficked up through neighbouring Uzbekistan.
Many believe the profits are helping fuel a growing boom in Mazar-e Sharif.
Again, no one names names, but as one Afghan official said: "Look at all the big new houses going up and all the new land-cruisers you see - - where's that money coming from?"
1 June Herat
Herat's governor Ismail Khan (left) has cracked down hard on drugs From Herat airport, the largest convoy of land-cruisers Mr Costa has had yet sweeps him into the city.
We drive straight through Herat and up a steep, winding road to an imposing, hilltop guest-house overlooking the city and its many ancient buildings.
Wearing his trademark black and white headscarf, Herat's powerful governor Ismail Khan appears to greet the UN drugs chief.
The two men walk into an ornate meeting hall, decorated with giant vases, antique weapons and murals depicting the Soviet invasion.
Much of old Herat was badly damaged during that time.
But it is striking how clean and well-kept Herat is now, compared to Kabul and other Afghan cities.
In contrast to the capital, most of the roads are tarmac-covered and potholes are rare.
Herat is also unusual for another reason - there is almost no poppy-growing in the surrounding province, according to UN surveys.
The governor takes a tough line on drugs and he has the power to enforce his will.
Few doubt that some opium and processed heroin is being smuggled through his territory to Iran - still the main transit country for Afghan drugs - but far less than through other provinces further south.
Mr Costa praises Ismail Khan's record, as heaps of water melon and fruit are served.
2 June Herat
The governor is keen to demonstrate the progress he is making here.
He takes Costa and his staff to the inauguration of a new road through the city. Lambs are slaughtered.
Then it is back to the hilltop guesthouse for Mr Costa's last meeting with regional governors, police chiefs and other officials.
Costa's message is the same.
The problem is growing. You have to do something, to protect your own and your country's reputation. And while Ismail Khan may have the drugs problem under control, many of his neighbours do not.
Sitting a few chairs down the table, the governor of Ghor province admits he is struggling, with an estimated 20,000 hectares of land sowed with opium this year.
Another governor raises a now common complaint about mixed messages coming from the central government, and from religious leaders.
In some eastern provinces - where poppy cultivation is well-established - he claims Friday prayer leaders have been telling their worshippers that it's legal to grow it, but not legal to use it.
But one of the elderly religious scholars invited to this meeting says there is no doubt that opium cultivation and production is against Islam.
He admits they need to do more to spread this message.
The last engagement of the day is to a drugs treatment centre in the city. Despite the governor's tough line, there are growing numbers of heroin addicts here.
It is a sign of how the Afghan drugs problem is affecting the country itself more and more.
There are over 250 people in the compound when I arrive, and staff say demand is rising all the time.
Many of the people at the centre are from as far afield as Kabul, where there is only one 10-bed drugs treatment centre.
This is not sophisticated treatment though, just "cold turkey".
It confines the addicts and keeps them away from heroin.
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