Blair told a joint news conference with Afghan President Hamid Karzai at the presidential palace in Kabul that British and NATO forces would likely remain in Afghanistan for years to come to prevent the Taliban's return to power.
"We came to Afghanistan because the sickness and the evil that was here came to us," Blair said, referring to the Sept. 11, 2001, attacks on the United States. "I don't believe there is an alternative but to fight this and to fight it for as long as it takes."
On his first trip to Afghanistan since 2002, Blair met with Karzai after visiting hundreds of troops at Britain's main southern base, Camp Bastion, in the restive southern Helmand province — a former Taliban stronghold and hub of the country's heroin trade.
"Here in this extraordinary desert is where the future of world security in the early 21st century is going to be played out," Blair said.
Britain has around 6,000 soldiers deployed in the country.
Blair's arrival followed a two-day visit to Pakistan, where he and Pakistani President Gen. Pervez Musharraf agreed to a package of joint ventures to tackle extremism and to aid war-ravaged Afghanistan.
Musharraf said neighboring Afghanistan needed a huge influx of reconstruction aid, similar to the U.S. Marshall Plan that helped rebuild Europe after World War II.
A total of 41 British soldiers have died in Afghanistan since the U.S.-led invasion in 2001 — including 36 deaths since Britain's deployment to Helmand province in July as part of the NATO mission to subdue insurgents and allow the expansion of reconstruction.
"This is a fight of a different kind from anything we have faced as a country, certainly in the postwar years," Blair said in Helmand. "It is not the same as two major powers fighting each other. It's not like World War I or World War II."
After talking with Blair, Maj. Andy Plewes said his company of commandos — newly arrived on a six-month tour — were eager to begin ousting insurgents and building relations with local community leaders.
"They've trained back in Britain for it and are ready to get out into the villages, sit down for talks with tribal leaders and drink endless cups of green tea," Plewes said.
British Defense Secretary Des Browne said last month that operations in Afghanistan had cost Britain $1.6 billion since 2001.
Aid for the region has included a program of offering loans worth around $190 apiece to farmers and rural workers, aimed at encouraging them to establish new businesses.
However, hopes of denting Afghanistan's narcotics trade were undermined by a bumper opium harvest this past season — enough to make 610 tons of heroin, more than the world's addicts consume in a year.
Officials have said next year's crop — which is already planted across swaths of southern Afghanistan — is likely to be about the same size.