Homeland Security Secretary Tom Ridge (search) raised the threat alert level Sunday for the financial sectors in Washington, D.C., New York and northern New Jersey.

Ridge said several targets have been specifically threatened: The World Bank and International Monetary Fund in Washington, D.C., the Prudential Building in Newark, N.J., and the Citigroup building and New York Stock Exchange (search) in New York City.

Ridge said the information came from multiple reports from multiple sources.

"Compared to previous threat reporting, these intelligence reports have provided a level of detail that is very specific. The quality of this intelligence, based on multiple reporting streams in multiple locations, is rarely seen and is alarming in both the amount and specificity of the information," he said.

Officials said that in the last 24 to 36 hours, intelligence operatives have received very specific information showing that Al Qaeda (search) has done very detailed surveillance on targets.

It was not immediately known what intelligence was leading the government to consider such action, and Ridge would not give any details about the sources of information. However, he was specific about the type of attack.

"The preferred means of attack would be car or truck bombs," he said. "That would be a primary means of attack."

A representative at the IMF press office said that U.S. authorities had informed them of the "high" threat level and they are taking the appropriate precautions. They said they will follow the federal government's recommendations. There is no word yet on whether or not the federal government has taken employee leave under consideration.

A World Bank official said Monday will be "business as usual" at the institution, however measures are underway right now to update employees, and the organization is putting up information for employees on their Web site and on a telephone help-line.

Law enforcement officials say that Al Qaeda planned to send terrorists across the Mexican border in to the United States to conduct suicide attacks in the city. Ridge said the alert status would remain in effect through Election Day, Nov. 2. Republicans are planning their national convention in New York between Aug. 30 and Sept. 2.

New York's status has remained at orange, indicating the second highest risk of terrorist attack, since Sept. 11, 2001, and a change to red would not mean dramatic changes in the city, said a Homeland Security official, who spoke on condition of anonymity.

A threat on financial institutions could have the impact of depressing stock trades on Wall Street on Monday, allowing terrorists to impact the U.S. economy. Ridge and other sources said Wall Street has made several changes to its security so that it can continue to operate even if it is attacked.

"The financial services industry since 9/11 has built in systems of protection and protection of the systems that help regulate and help control equity markets, the flow of currency around the entire world," he said.

Ridge said that it is up to Mayor Bloomberg to change the entire city's status to red, but right now the threat alert is specific to the financial institutions.

"[New York City officials] will be working particularly with those companies at these locations, taking a look at vulnerabilities ... I don't think [Bloomberg] is necessarily going to take the city up," Ridge said.

Bloomberg told reporters in an afternoon news conference that though the city has been on high alert all along, the presence of police on the street and in the subways will be even higher than it was.

"We are deploying our full array of counterterrorism resources. We will spare no expense and we will take no chances. We will be watching and protecting the city through never-ending vigilance," Bloomberg said.

Bloomberg added that employees should get up and go to work and "continue to enjoy the freedoms that the terrorists find so threatening."

"For them, there is nothing different this Monday than there was last Friday," he said, adding that nothing political is motivating the change in alert status.

In a separate press conference, New Jersey Gov. Jim McGreevey (search) said the state has enhanced vehicle inspections, has state police riding public transport, has been working with the financial services sector to conduct employee "identification checks," is restricting building access, including increased monitoring of parking garages, and has increased its statewide bomb squad and K-9 units for surveillance.

Sid Caspersen, director of New Jersey's Office of Counterterrorism, said his agency has been working since May to implement a number of initiatives throughout the state in preparation for such an event.

"So even though it was new to the news media and new to the public, it is not new to us. We have been aware that Al Qaeda has been potentially targeting us so we have been doing a number of strategic initiatives with every municipality where we have identified potential targets," Caspersen said.

Prior to Sunday's status change, Washington and the rest of the nation were on yellow alert, or elevated status of risk; that is in the middle of the five-color scale.

'Excruciating Details' Led to Alert

White House spokeswoman Erin Healy said President Bush approved of Ridge's increasing the threat level after hearing about intelligence that was "very new, coming in during the last 72 hours."

"The president made the final decision today agreeing with the recommendation of Secretary Ridge to go ahead and raise the threat level in these select areas," Healy said.

Government officials said the new intelligence came in "excruciating detail" and indicated meticulous planning that matched the methods of Al Qaeda. One government official identified explosives as the likely mode of attack, as opposed to a chemical or biological attack or a radiological "dirty" bomb.

The intelligence showed that terrorists had been measuring the security around the sites named, including tabulations on the flow of pedestrians; the best places for reconnaissance; how to make contact with employees who work in the buildings; construction of the buildings; traffic patterns; locations of hospitals and police departments; and which days of the week present less security at these buildings.

Specifically, one official said the intelligence showed that Al Qaeda had learned that midweek pedestrian traffic equaled 14 people per minute on each side of the street for a total of 28 people; that some explosives might not be hot enough to melt steel; and that the construction of some buildings might prevent them from falling down.

The senior intelligence official who spoke on condition of anonymity said he had not seen such extraordinary detail in his 24 years in intelligence work.

A Winding Trail of Terror?

Ridge said the latest warning is not linked to the July arrest in Texas of a Pakistani woman accused of illegally crossing into the United States. Law enforcement accounts indicate she had an altered South African passport along with $7,000 in cash and an airline ticket to New York.

U.S. law enforcement authorities say they believe crime syndicates within the South African government are selling illegal passports for as little as $77 apiece.

The woman, Farida Goolam Mohamed Ahmed, 48, traveled from Johannesburg through Dubai, United Arab Emirates, to London and on to Mexico City. Authorities said she later told them she was smuggled into the United States from Mexico by crossing the Rio Grande.

Authorities say Ahmed's name appeared on an FBI watch list and it surfaced during an investigation of an overseas terrorist incident. Homeland Security officials have warned that Al Qaeda could use women and non-Arabs as operatives to avoid detection.

Rep. Solomon Ortiz, the ranking Democrat on the House Armed Services Subcommittee on Readiness, said "very credible" people told him Ahmed has traveled within the United States more than 250 times.

A senior official at U.S. Border Patrol told FOX News that a culmination of several pieces of information led to the increased threat alert. That included the arrest of Ahmed, but she was not key to the raised alert.

Ahmed's court-appointed attorney said his client is not charged with any terrorist activity and does not have a criminal record. However, she was denied bond on Tuesday.

The U.S.-Mexico border (search) is an area of concern to congressional members as well as U.S. officials. Sen. Joe Biden, D-Del., said in the War on Terror, more efforts are needed to reduce vulnerabilities along the border.

"Some progress has been made under border security, but we haven't implemented" enough measures, Biden said. "We should be focusing on a line that is clearly drawn here on Earth. They relate to borders, they relate to rails, they relate to 101 nuclear power plants that exist and we're doing woefully little on any of those things."

Biden, the ranking Democrat on the Senate Foreign Relations Committee, said Al Qaeda knows all the prime targets it wants to hit in the United States. Ridge has pointed out before that Al Qaeda has to be right or lucky once to carry out an attack, but U.S. officials have a much heavier burden. To prevent an attack, they must be right all the time.

New York City police officials have warned businesses in the city to take extra precautions at work, including checking employee identification cards and updating emergency plans.

It also gave some things to look out for, including unanticipated deliveries or maintenance work, people taking unusual video or photographs, and visitors claiming to be lost or looking disoriented. The warning also said bomb threats may be used to evaluate emergency response time.

Fox News' Kelly Wright and Anna Stolley and The Associated Press contributed to this report.