LONDON - A key al-Qaida operative suspected of authoring surveillance documents that sparked terror alerts in the United States was among 13 terror suspects arrested in Britain, an official said.

The documents of surveillance of five U.S. financial institutions were found on the computers of two accused members of Osama bin Laden's terror network arrested in Pakistan last month. Pakistani intelligence officials told The Associated Press the computers also held images of London's Heathrow, Airport and that this information was passed to British officials.

The revelations draw a link between two major sweeps against suspected al-Qaida networks in Pakistan and Britain - as well as the alerts announced Sunday in New York, New Jersey and Washington.

At least 20 people have been detained in Pakistan in the past month, and Britain is holding 12 men from raids on Tuesday after releasing one person. British police on Thursday announced the arrest of another man, wanted in the United States for allegedly helping finance terrorist activity.

Among the 12 held in Britain was a senior al-Qaida member, known as Abu Eisa al-Hindi or Abu Musa al-Hindi, who the official said is suspected of having written the surveillance reports detailing security, construction and other features of the five U.S. financial buildings.

The official called al-Hindi "a key al-Qaida operative." A counterterrorism official, speaking on the condition of anonymity earlier this week, said much of the documentary evidence for the alerts, including surveillance reports, was in fluent English, indicating the author spent significant time in the West.

The terror alert concerned the Citigroup Center Building and New York Stock Exchange, the Prudential Building in Newark, and the International Monetary Fund and World bank in Washington.

Maps, photographs and other details of possible targets in the United States and Britain were found on computers belonging to Ahmed Khalfan Ghailani - a Tanzanian indicted for his role in the 1998 bombings of U.S. embassies in East Africa - and a Pakistani computer expert identified as Mohammed Naeem Noor Khan, said two Pakistani officials, who spoke on condition of anonymity.

Much of the information was at least several years old, some of it preceding the Sept. 11, 2001, attacks, U.S. officials have acknowledged, though some of it may have been updated as recently as January.

Khan was arrested by Pakistani forces on July 13, followed by Ghailani's arrest on July 25.

The CIA provided information that contributed to the detention of al-Hindi, as well as information that led the Pakistanis to detain Khan.

The Washington Post and British papers said al-Hindi was also suspected in plotting an attack on Heathrow, Europe's busiest airport.

A Lahore-based intelligence official involved in the investigation following the July 13 arrest of Khan said his computer contained photographs of Heathrow airport, as well as pictures of underpasses that run beneath several buildings in London.

Earlier, Peter Hain, leader of the House of Commons, told British Broadcasting Corp. radio that those detained Tuesday "are important arrests" but declined to comment on reports of a plot against Heathrow.

"If we had evidence of a specific threat, then we would tell everybody," he said. "Now the situation is not that at this stage."

A Heathrow spokeswoman said airport authorities had not heard anything from the government "to suggest the threat level to Heathrow has increased in recent weeks."

British police also said Thursday they had arrested a British man, Babar Ahmad, wanted on terrorism charges in a warrant issued by a federal prosecutor in Connecticut, and that anti-terror officials were searching three "residential premises" and one business in southwest London on behalf of U.S. authorities.

Ahmad, 30, is accused in the United States of trying to raise funds for "acts of terrorism in Chechnya and Afghanistan" from 1998 through 2003, according to the U.S. extradition warrant. His detention was not believed to be linked to the arrest of the 12 on Tuesday.

A U.S. official, speaking on condition of anonymity, said the United States expects to seek Ahmad's extradition from Britain but noted that such requests typically take years. Some of the Web sites Ahmad is accused of running to solicit money were operated out of Connecticut, the official said.

Heathrow has been at the center of terrorism fears before.

In February 2003, the government deployed tanks and troops there after police warned that al-Qaida might try attacking London. Officers searched cars, vans and boats in towns under the airport's flight path. Police even considered closing the airport.

In March, 1994, the Irish Republican Army fired a dozen mortar shells at Heathrow in three attacks within days of each other. None exploded, but flights were severely disrupted.