By Andrew North and Bilal Sarwary
BBC News, Kabul and Kunar
US forces clear an area - but then militants return
As the US military's battle to subdue the Taleban and other rebel groups in Afghanistan moves into its fifth year, one eastern province bordering Pakistan has increasingly become a symbol of its difficulties.
Despite several major American offensives in Kunar over the past year, the militants keep re-grouping - many of them foreign fighters with al-Qaeda backing.
The trouble it has had in this area has led US forces to use psychological operations, or 'psy-ops' tactics, that one US human rights group alleges could have broken the Geneva conventions governing armed conflict.
US troops have been broadcasting messages which Human Rights Watch says implicitly threatens "collective punishment" for people of the valley.
It was in Kunar that US forces suffered their worst single loss of life in Afghanistan since they first invaded in 2001 in response to the 9/11 attacks.
One of their helicopters was shot down in late June, killing
all 16 special forces and crew on board.
The situation there bears comparison with that facing US troops in western Iraq battling Sunni rebels and al-Qaeda militants - although casualties there are far higher.
Every time they try to clear an area, the insurgents move elsewhere and then return when the Americans have gone.
That is what militant groups have been doing all year in Kunar, according to local officials and residents of the province who spoke to the BBC.
The difficult, high altitude terrain is on their side. So too, say these officials, is the presence of a nearby safe haven - the tribal areas of neighbouring Pakistan.
They say many militants fled there after the most recent nine-day American offensive in late November.
In a press release about Operation 'Sorkh Khar' - which translates as Operation Red Donkey - the US military described it as a "success" in dominating "the enemy in what has been a staging area in Kunar."
But residents and officials in the province - who asked not to be named because of security concerns - said many insurgents had now returned.
The stronghold of these groups - and the focus of many US operations - has been the steep, forested Korengal valley, to the north-west of the provincial capital, Asadabad.
The high terrain helps the insurgents
It was here that the US Chinook helicopter was shot down on 28 June, after being sent in to rescue a special forces unit on the ground whose mission had been compromised.
Three members of that four-man team were also killed.
The valley has become a kind of meeting place for anti-American militants of all shades. "Enemy central" in the words of one US soldier who's been there.
Local officials have said for some time that supporters of the Taleban and al-Qaeda have been increasingly working together there.
They also co-operate with militants from Hizb-e Islami Gulbuddin, a group led by hardline Islamist former mujahideen commander and one time Afghan prime minister Gulbuddin Hekmatyar.
His whereabouts are unknown, but he is one of the key targets of US forces in the region.
So too is the man said to be al-Qaeda's leader in Kunar, an Arab called Abu Ikhlas al-Misri, who fought the Russians in the region during the 1980s and has lived there ever since, marrying locally.
In turn, he is believed to work closely with a Taleban commander known as Ahmad Shah, who US commanders believe was involved in bringing down the helicopter.
US 'not letting go'
Add to this difficult mix "criminal activity", according to Lt-Col Jerry O'Hara, chief spokesman at the US military's main operational base Bagram - with many people involved in smuggling "drugs, timber and gems".
But the US is not losing in Kunar or its Korengal valley in particular, he insists.
"We're not letting go of that area."
But in the long term, he says, "the solution there is not going to be a military one. It's about the Afghan government and security forces taking over."
One tactic US forces have recently tried is to broadcast messages on local radio in the name of Kunar's governor calling on Korengal residents to expel "enemy fighters living in their areas".
It's all part of an approach used nationwide by the US-led coalition, to try to undermine support for militants in these areas.
And despite the intense militant activity in Kunar, Afghan officials say many people there only provide support under
Human rights fears
The BBC obtained a copy of one broadcast from officials in the province who requested anonymity.
They said they had been given the message by American personnel from a local base and believed that is where it had been written, even though it was in the name of the governor and his deputy.
This is how it ends:
"if they [the people of Korengal] are not going to comply with the demands of expelling the enemy from their villages then we will be forced to continue to pursue the enemy relentlessly until the elders either force them
to leave or the hand of our national security troops force them out. The people of Korengal are either with the people of Kunar or against them."
However, when asked about the message, the US military said it was not their work.
"I am told we did not write this document; that it was written by the governor," said Lt Colonel Laurent Fox, a spokesman at its headquarters in Kabul, in an e-mailed response.
However, his statement confirmed that US troops had put it out.
"I was told that CJTF-76 (the operational name of the US-led coalition force in Afghanistan) did transcribe it after it came out and ran some messages based on this letter on Peace radio in that area."
But according to Human Rights Watch, regardless of the
document's original authorship, broadcasting the message to the people of Korengal could break international conventions.
"It contains a barely veiled threat of collective punishment," said Sam Zarifi, its research director for Asia. "Making such a threat is a violation of the Geneva conventions and other laws of war."
Lt Colonel Laurent Fox said the aim of transmitting the message was to use "non-lethal means against anti-government personnel."
However, some Afghan officials involved in disseminating the broadcast said they were not happy about the language, which they described as "how the foreigners speak".
"It will make things worse," another warned.