According to officials of the city's police department, police officers will be out in force, conducting random bag searches and patrolling the city's subways. Officials for the rest of the city 's mass transit systems said they will increase security guards on trains and at commuter hubs like Grand Central and Penn Station.

The Metropolitan Transit Authority, the agency in charge of public transit, is also adding security to bridges and tunnels in the city.

According to Police Commissioner Ray Kelly, these measures are just a precaution, because officials are still investigating whether the attacks are part of a global plot.

"In an abundance of caution, we're going to add additional personnel and additional resources to the system," Kelly said.

New York Mayor Michael Bloomberg also urged the New Yorkers not to worry and trust and continue going along with life as normal.

"Let me reiterate, there is no evidence suggesting that New York City is a target, but as we all know vigilance is the reality of the post-9/11 world," he said.

Meanwhile, the death toll continues to rise in Mumbai after several explosions in the city's train system during the evening rush hour Tuesday.

Indian officials say at least 147 people are dead, and more than 400 injured.