Kabul - British Prime Minister Gordon Brown said Monday in Kabul that the world could not tolerate the existence of terrorist bases in border areas of Afghanistan and Pakistan, saying a new strategy would be unveiled this week.

Brown arrived on a surprise visit in Afghanistan on Monday morning and met with President Hamid Karzai to discuss his plans to fight the "crucible of terrorism" in the border region, to be formally announced in the House of Commons this week.

"Stability of the streets of London depends on stability of the border areas of Afghanistan and Pakistan," Brown told a joint press conference in Karzai's presidential palace.

"These border areas between Afghanistan and Pakistan are the breeding ground, the crucible of terrorism," he said. "A chain of terror links these areas to the streets of many capital cities of the world."

Brown said Britain would help strengthen Afghan security and would cooperate with Pakistan authorities to deal with "terrorists and terrorist threats in their area."

Tribal areas in Pakistan bordering Afghanistan have been a weak spot in the fight against the Taliban and al-Qaeda networks.

Afghan and NATO military officials say militants retreat to rear bases inside Pakistan after attacks in Afghanistan.

Karzai told the press conference that "terrorists" were defeated in Afghanistan in 2001, when the Taliban regime was ousted in a US military invasion, but said that NATO and US forces were needed to continue fighting them.

"Security is an area where we still have problems," he said, adding, "It is not the return of the Taliban, it is the continuation of the threats that we are facing that we are trying to remove and defeat."

"The question of existence of the terrorism in the region, their sanctuaries, their holding grounds their sources of finance and all that enables them for whatever reason to launch attacks in Afghanistan or in Pakistan or in the rest of the world."

Earlier in the day, Brown traveled to southern Helmand province, where he met with provincial authorities and British troops.

"There is a crucible of terrorism in the mountainous border between Afghanistan and Pakistan," Brown told soldiers in Camp Bastion in Helmand province. "Our approach to these countries is different, but must be complementary."

About 8,300 British troops are stationed in Afghanistan, mostly in Helmand. London plans to send 700 additional soldiers to the country to provide security for the August presidential election.

Brown was scheduled to visit Islamabad later on Monday. (dpa)