At the World Trade Center site, where nearly 3,000 people lost their lives almost 10 years ago, Mayor Michael Bloomberg and other public officials expressed their gratitude on Monday that America had fulfilled its commitment by bringing Osama bin Laden to justice.

"Osama bin Laden is dead, and Lower Manhattan is pulsing with new activity," Bloomberg said. "Osama bin Laden is dead, and New York Citys spirit has never been stronger."

Against the backdrop of jackhammers working in the background on the new National September 11 Memorial buildings that are under construction, the mayor and other officials paid tribute to the victims of the terror attacks the day after it was announced that bin Laden was killed.

The mayor said his thoughts immediately went to those who lost their lives, as he heard the news on bin Laden's death yesterday.

"In the dark days that followed September 11th, we made a solemn commitment – to the dead and the living – that we would bring to justice those responsible for killing more than 2,900 innocent people," he said. "Yesterday, Osama bin Laden found out that America keeps its commitments."

He added, "We are rebuilding from the ashes and the tears a monument to the American spirit. New York's way is ever forward, ever skyward."

The mayor acknowledged that bin Laden's death changes little in substituting New York City as  a "top target" for terrorists, and that the highest priority mission remains to defend "our city and country against all those who use violence to attack freedom."

Police Commissioner Ray Kelly, together with Port Authority and the Metropolitan Transportation Authority officials, joined the mayor at the press conference and outlined measures taken to insure the city's safety in the wake of bin Laden’s death.

"Our assumption is that bin Laden's disciples would like nothing better than to avenge his death by another attack," Kelly said. 

Kelly said police presence has been increased during rush hours, heavily armed forces have been posted at Times Square, Financial District and key transit hubs, and there are additional emergency services and helicopters conducting patrols in the city. The police was also working with its federal partners in checking whether any signs of retaliatory attacks could be identified.

Earlier in the day, MTA spokesman Jeremy Soffin said it was too soon to generate hard ridership data on the morning commute but the authority "didn't notice any drop-off."

Commuters streamed off Metro North trains and through the main concourse of Grand Central Station Monday morning much like any other.

"It's good to see some tangible results," said Phil Seiter, a 28 year-old hedge fund worker, as MTA policemen strolled past with a bomb-sniffing dog. "Even though we've taken out other Al Qaeda operatives, bin Laden is the face of terror. It's good to see him go down."

Several commuters said they'd noticed extra police at Grand Central, which had made them more alert to their surroundings. Others expressed anxiety about possible retribution in the form of more terrorist attacks on the United States -- and obvious targets like Grand Central.

"It was interesting walking across the station this morning and looking at the security forces," said Luke Doherty, an advertising executive. "Now in these areas, do you have to pay a little bit more attention than you did yesterday?"

He added: "There's relief that one part of it is over but uncertainty about what comes next."

With reporting by Jim O'Grady