Police in Washington, New York and New Jersey have tightened security around key financial institutions after homeland security officials warned of a possible al-Qaida terror attack. Officials urge residents to go about their daily routines despite heightened concern

In New York City, northern New Jersey and Washington, D.C., heavily armed security officers are guarding key financial institutions. The extra security was ordered by the Department of Homeland Security on Sunday after officials said the buildings were specifically mentioned as targets of a planned terrorist attack.

To prevent a possible car or truck bomb, police have blocked off some streets and barred large trucks from crossing bridges that lead to lower Manhattan.

The United Nations also added security officers around its building on midtown Manhattans east side, according to U.N. spokesman Fred Eckhart.

"On the advice of the New York City police department, we have further tightened our security measures over the past weekend," he said.

Meanwhile, government officials encouraged people to go about their business.

New York governor George Pataki and mayor Michael Bloomberg rang the opening bell at the New York Stock Exchange. The mayor said New Yorkers are not afraid.

"New York City is not going to be cowed by the terrorists, make no mistake about that," said Mr. Bloomberg. "We're not going to spare any expense in protecting us, but also the people of New York City know that giving in to terrorism is exactly the wrong thing to do."

On Wall Street, Senator Charles Schumer shook hands with workers and thanked them for coming to work.

"The terrorists want to scare us," he said. "If every time they made a threat, we stopped doing what are doing, they'd win. So we feel it is almost a moral imperative for everybody to go about their jobs. There may be a few butterflies in some stomachs but you still move forward."

Some employees reporting to work at the Stock Exchange and in Washington at the World Bank and International Monetary Fund admitted feeling nervous.

A New Yorker says that since the terror attacks of September 11, 2001, tight security is nothing new

"Should be fine, no problems," he added. "We've been through this before. Should be okay. Another day in New York!" On Monday, U.S. Treasury Secretary John Snow promised that "extraordinary measures" are being taken to protect against the terror threat.