In warren-like streets of Karachi, influential Muslim religious schools and mosques swear allegiance to militant Islam worldwide, in what one former Pakistani general calls an axis of hate against the United States.

It was in Karachi, a teeming city of more than 14 million people, that police and intelligence agents Wednesday captured one of the world's most wanted men -- Ramzi Binalshibh, U.S. officials said.

Binalshibh was a roommate of hijacking leader Mohamed Atta in Germany; the FBI believes he was originally intended to be the 20th hijacker before he failed to enter the United States.

His capture confirmed suspicions that many of the key figures from Al Qaeda have sought refuge in Karachi, a turbulent, crime-ridden, cosmopolitan city with longtime ties to the Middle East and with the easiest air and sea connections abroad.

Karachi is Pakistan's main port and premier metropolis, a sophisticated center of international business and commerce which served as Pakistan's first capital until it was moved to Islamabad in 1962.

However, it is also the country's crime center. Violence and the fear that Islamic militants are increasingly targeting Westerners have prompted many Americans, Britons, Germans and others to leave. Foreign consulates have either closed or scaled down their staffs.

Early this year, the city's doctors staged a series of one day strikes to demand police protection after 13 doctors, most of them minority Shiite Muslims, were slain in a series of attacks.

Karachi is also a center of Islamic militancy in Pakistan, a place where "holy warriors" on the run can find like-minded people willing to help with safe houses, false papers, money and protection.

The city is also notorious for criminality, especially kidnappings and sectarian murders in which extremists from rival Muslim groups target members of other sects for assassination.

It was in Karachi that Wall Street Journal correspondent Daniel Pearl was kidnapped in January. His body was found four months later in a shallow grave on the edge of the city.

In May, a car bomb at the city's Sheraton Hotel killed 11 French engineers and three other people, including the suicide bomber. One month later, 12 Pakistanis died when a car bomb exploded at the U.S. Consulate.

At the heart of Karachi's Islamic militant community is a network of Muslim religious schools, or madrassas, where respected clerics promote a brand of Islam little different from the one mandated by the Taliban when they ran Afghanistan.

Many Taliban leaders, in fact, were graduates of madrassas in Karachi, Peshawar and other Pakistani cities.

At Karachi's Banuri Town madrassa, each of the 10,000 students is taught to be a supporter of Al Qaeda and the Taliban. The school's headmaster, Nizamuddin Shamzai, said in a recent interview that students are taught that a good Muslim helps his friends evade capture.

Several other major madrassas in Karachi, including Jamia Farooquia, have remained centers of pro-Taliban and Al Qaeda sentiment. The headmaster of Jamia Farooquia, Maulvi Saleemullah Khan, was a close friend of Taliban leader Mullah Mohammed Omar and a frequent visitor to Afghanistan during Taliban rule.

So influential are the madrassas within Pakistan, where more than 95 percent of the 145 million people are Muslims, that for security forces or the police to enter the grounds in search of Al Qaeda fugitives would cause a huge public backlash.

In an interview with The Associated Press before he left for the U.N. General Assembly, Pakistan President Gen. Pervez Musharraf said Al Qaeda members fleeing Afghanistan had infiltrated beyond the remote tribal area along the border and were turning up in Pakistan's cities.

Once in the cities, many of them have forged ties with Pakistani extremist groups such as Jaish-e-Mohammed, Harkat-ul-Mujahedeen and Lashkar-e-Tayyaba, which Musharraf has banned. Most of the major extremist groups have extensive networks in Karachi.

Retired Pakistani Gen. Anwar Sher said that the alliance between Al Qaeda and Pakistani extremist groups was an "axis of hate" directed against the United States -- and by extension against Musharraf.

Musharraf's decision to align Pakistan with the United States made him a marked man as far as militant Muslims are concerned.

"Musharraf is working for America," said Muslim cleric Mohammed Asad Thanvi, a member of the privately run board that governs Islamic religious schools in Pakistan.