The UK and Pakistan have agreed to strengthen their ties to fight terrorism following talks between the countries' two leaders in Lahore.
Prime Minister Tony Blair and President Pervez Musharraf agreed that restoring order in Afghanistan was crucial.
Mr Blair praised Pakistan's co-operation. The president said his country was doing all it could to help.
But he added that defeating the Taleban could not be done by force alone and said a "broader strategy" was needed.
'Marshall Plan' call
He urged a "massive inflow" of development aid to rebuild the south-east of the country - the centre of the Taleban insurgency.
He likened the effort needed to the US Marshall Plan to reconstruct Europe after World War II.
"There is a requirement for a massive inflow of development funds [into Afghanistan]"
Mr Blair pledged a commitment to battling the Taleban, saying: "Nobody should be in any doubt at all about our commitment to Afghanistan."
It was of "fundamental importance" to global security "to stick with it and see the job through," he said.
Mr Blair's official spokesman later said Britain had always pursued security alongside reconstruction in Afghanistan, and the problem was not funds but getting security and infrastructures in place.
Pakistan's co-operation in cracking down on cross-border infiltration by Taleban militants is seen as critically important for the success of US and Nato military operations in Afghanistan.
Gen Musharraf said: "The Taleban problem is an Afghan problem. It is in the south-eastern region of Afghanistan, being supported by elements from this side," he said.
In pictures: Blair in Pakistan
"We need to put our house in order here on our side and make sure that this support is cut off. But the main battle is in Afghanistan."
The BBC's political editor Nick Robinson said: "The prime minister has heard warnings here in Pakistan that the war in Afghanistan will not be won simply through military means.
"Nato's own commander says the next few months will be vital.
"With questions growing about the war in Iraq, he can ill afford to have another war described as pretty much a disaster."
Aid doubled
The president also said he believed resolution of the Palestinian dispute was at the "core" of the fight against terror, adding Mr Blair "agrees totally with me".
"Nobody should be in any doubt at all about our commitment to Afghanistan"
Mr Blair said the UK would double its development aid to Pakistan to £480m ($960m) over the next three years.
Much of this will go to the reform of the Islamic religious schools, or madrassas, some of which have been accused of encouraging extremism.
This reflects concerns a generation of young British Muslims are being radicalised through contact with militants in Pakistan.
There will also be a counter-terrorism package of technical assistance, worth some £8m ($15m), UK officials said.
Describing the weekend's talks as "immensely constructive", Mr Blair paid tribute to the president's "courage and his leadership" in taking Pakistan on "this journey of change and modernisation".
He said relations with Pakistan were at "their highest point for many years".
Intelligence service row
The leaders' expressions of unity follow a leaked British report in September, which claimed Pakistan's intelligence service, ISI, had indirectly helped the Taleban and al-Qaeda.
Mr Blair assured Gen Musharraf at the time that the report, by a naval commander at the Ministry of Defence, did not reflect his government's view.
Gen Musharraf rejected the claims, and said ISI's support was vital.
Following the talks with Gen Musharraf, Mr Blair returned to the capital, Islamabad, where he visited the Faisal Mosque and met moderate Islamic religious leaders.
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