Seven years on from the 9/11 attacks on New York and Washington, BBC correspondents report on why the key stronghold of groups linked to al Qaeda is now the region straddling the border between Pakistan and Afghanistan.
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Alastair Leithead, Camp Bastion, Helmand province, southern Afghanistan:
British troops have faced tough fighting throughout the summer
The three-day dust storm has finally cleared and with it the temperatures here in the British desert base in Helmand are finally starting to drop.
The men of the Parachute Regiment are coming to the end of their second tour to southern Afghanistan, and it's been another tough summer of fighting insurgents and making little tangible headway.
Many of the 8,000 or more British forces in southern Afghanistan are living out in the remote bases scattered through this violent province, and much of their time is spent patrolling, clashing with the Taleban and then returning to back base.
Even when big operations take ground it's almost impossible to hold, as the Afghan security forces are still being built.
The Paras may be leaving, but it won't be long before they are training for their next deployment to Helmand - there's a growing sense the troops will have to be on the ground for a long time to make any lasting difference.
The idea is to improve security to create the space for the government to take a firmer grip and to use development projects to win people over.
But there's little sign of the security improving - the open border and the sanctuaries in Pakistan allow fighters with better training to cross over and carry out ambushes, plant bombs and dispatch suicide bombers.
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Lyse Doucet, Kabul, Afghanistan:
An increase in attacks in Kabul has led people to flee the city
There is a new worry in Kabul: the Taleban now lie in wait just beyond its gates. Many of the main roads, rebuilt with great fanfare, are now too dangerous to drive on. To head south from Kabul is to run a gauntlet of threats from Taleban fighters or its allies.
In recent days, there have been reports of violence, kidnappings, and in the dark of night in Kabul, the last silence before morning prayers was shattered by the thud of rockets landing in this city.
Few believe the Taleban can take over Kabul again. But it's a challenge for Afghan forces who recently took over from foreign troops responsibility for protecting this capital.
When we visited the northern and southern approaches, Afghan police and soldiers were on guard. That's also concentrating minds in the heavily fortified Presidential palace. President Karzai was at pains to be diplomatic when we met for an interview.
He, like most people here, has long believed tackling the Taleban means taking on their sanctuaries across the border in Pakistan.
He expressed hope that with a new President on the other side, and a more forceful approach in Washington, the two neighbours could work together to confront a common threat. But it certainly won't be easy.
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Owen Bennett-Jones, Islamabad, Pakistan:
Owen Bennett-Jones has visited the heart of the tribal area
There have been a number of American strikes in the border areas in the last few days, which have upset many people, although I have yet to see any street protests.
However, I think there is no doubt that if the Americans came in in a very public and overt way, with troops on the ground in significant numbers, there would be an almost unanimous rejection of that approach.
It would also stir up the tribal areas. I have just come back from Khyber, talking to some of the tribal elders there and they are absolutely clear that if they are presented with a choice between the Taleban and America, they will choose the Taleban.
They will see it as an attack on Islam.
There is rampant anti-Americanism here and that does suggest that America is losing the battle for hearts and minds.
When I spoke to Pakistan's Foreign Minister, Makhdoom Shah Mahmood Qureshi, he said such attacks were unproductive and alienated the local population.
Pakistan's new President, Ali Asif Zardari, has only been in the job a few days and he is already finding out how difficut it is to run the country.
He's got the Americans asking him to fight harder - he says he is fighting hard.
He's got the army suspicious that he is too pro-American and may have given the green light to some of these recent attacks, which would explain why the army chiefs came out saying this is absolutely unacceptable.
And he's also got public opinion which is rampantly anti-American, so it's quite a difficult job being President of Pakistan.
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Haroon Rashid, Islamabad, Pakistan:
Haroon Rashid (r) has been reporting from Waziristan
There is a new breed of Taleban, which is known in northwestern Pakistan as the "local Taleban". It is composed mostly of Pakistanis, but also includes some Afghans.
This Taleban also has links with Al Qaeda, harbouring some of their foreign militants and foreign-national leaders.
The problem is that the Pakistani government has been finding it difficult to control them and prevent them spreading their influence to a large parts of Pakistan.
In addition to the Taleban and Al Qaeda, there are also many sectarian groups within Pakistan.
Some of these are under the leadership of the Taleban Movement of Pakistan, led by Baitullah Mehsud, but there others who disagree with him and choose to keep their own identities.
These splinter groups are responsible for sectarian violence, such as that taking place in Kuram, where Sunni and Shia are fighting each other.
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James Coomarasamy, Washington, United States:
America's military action inside Pakistan has caused anger
On the day when the Pentagon became the site of America's first national monument to the September 11th victims, both the man who led the dedication ceremony, President Bush, and those who work inside the building, are shifting the focus of their war on terror.
On Wednesday, the Chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, gave Congress a sombre, downbeat assessment of US efforts to counter Taliban and Al Qaeda influence in Afghanistan.
He signalled a change of military strategy, to encompass raids on militant enclaves in the tribal, border areas of Pakistan.
Meanwhile, evidence is mounting that Washington is committed to taking this kind of action unilaterally, even at the risk of angering the Pakistani military, which, US intelligence believes, is more inclined to help, than hinder the militants' cause.
Washington appears to be stepping into a diplomatic cauldron and, in the process, complicating the nascent presidency of Asif Ali Zardari, but it seems the Bush Administration has concluded that it has no other options.
So, as the two men vying to be the next Commander in Chief suspend their campaigning, to attend memorial ceremonies, Barack Obama and John McCain will be reflecting on the increasingly complex military, political and diplomatic situation in Afghanistan and Pakistan that one of them will inherit next January.