( CNN ) -- As the nation enters the weekend marking the 10th anniversary of the September 11 attacks , law enforcement authorities are deploying additional security measures and urging all Americans to be vigilant for suspicious activity . Much of the beefed-up security has been in the planning well before Thursday 's announcement of a potential al Qaeda vehicle bomb plot against New York City or Washington , officials said . And some of the toughened measures wo n't be visible to the public , officials said . At the U.S. Capitol , Americans can expect to see `` visible strategic security enhancements '' such as more uniformed and undercover officers and more police cruisers , as well as deployments of bomb squads , Hazmat and SWAT teams , and K9 units , said Sgt . Kim Schneider of U.S. Capitol Police . Federal law officials will be sharing information and coordinating operations , Schneider said . For example , Capitol Police special agents are embedded in the intelligence community and assigned to the FBI , Secret Service and Department of Defense , Schneider said . The efforts are designed `` to present a visible deterrent to our adversaries and detect those who may present a threat '' as well as `` to respond to incidents in our jurisdiction or take protective measures in response to an incident occurring elsewhere in the National Capital region or anywhere around the nation , '' Schneider told CNN in an e-mail . `` People on the Capitol Grounds or in the area of the U.S. Capitol may notice a more visible presence in addition to the multiple layers of security that are not visible to the public , '' Schneider said . Many additional security measures were stepped up Friday in the wake of U.S. intelligence gathering about an al Qaeda-organized vehicle bomb being detonated in New York City or Washington on the 10th anniversary , which falls Sunday , authorities said . In New York City , officers were stopping and searching trucks as they approached the George Washington Bridge , which links New Jersey with New York City , as well as the Queens Midtown Tunnel , the Holland Tunnel and the Verrazano Bridge , linking Staten Island and Brooklyn . Police also manned checkpoints throughout Manhattan where they examined vehicles , particularly vans and trucks , for possible bombs . In Washington , where increased police activity began after Labor Day , members of Congress , their staff and visitors were being urged Friday to continue their vigilance for anything suspicious , authorities said . `` Remember , 'if you see something , say something ! ' '' said Wilson Livingood , the U.S. House sergeant-at-arms . The al Qaeda threat has yet to be corroborated , White House press secretary Jay Carney said . National security officials have `` been running a process for four months , anticipating the need to be extra vigilant , to take extra precautions around this anniversary , the 9/11 anniversary , because , as you would expect , al Qaeda , while it lost its leader when we brought justice to Osama bin Laden , remains a threat to Americans , remains interested in attacking the United States and Americans , and we have to be vigilant against that threat , '' Carney said . Vice President Joe Biden urged all Americans to be wary this weekend . `` Continue your life as normal . Be vigilant . Be vigilant , '' Biden said on NBC 's `` Today '' show Friday . `` Report anything that looks suspicious to you . And you know , we went through this before in a different circumstance with the car bomb ( attempt ) in Times Square ( in 2010 ) . There are people who are likely to try over the next period of months and years , but the point is that we are using every single asset we can , including local law enforcement , to help thwart the possibility it could happen . '' Some intensified security measures will be out of the public eye , Homeland Security Secretary Janet Napolitano said . `` Our security posture includes a number of measures both seen and unseen , and we will continue to respond appropriately to protect the American people from an evolving threat picture both in the coming days and beyond , '' she said in a statement . In Washington 's subway system , police were conducting random baggage tests Friday as commuters came down the escalator -- measures that were previously planned and were n't a result of the potential al Qaeda threat , said Michael Taborn , the transit system 's police chief . Dog teams patrolled platforms , and an officer with a flashlight examined tracks after trains passed . Washington , D.C. , Mayor Vincent Gray said Friday the city is `` redoubling '' its security efforts in the wake of the unconfirmed al Qaeda threats , with officers working 12-hour shifts and operating under a restricted-leave policy . `` We take these threats seriously -- as we do all threats to our city -- and citizens should know we are taking all the appropriate steps to ensure their safety , '' Gray said in a statement . CNN 's Mike Ahlers , Ted Barrett , Sarah Chaffin , Paul Courson and Jay McMichael contributed to this report .
All Americans need to be vigilant to suspicious activity , officials say . SWAT teams , bomb squads and K9 units are deployed in Washington . Some toughened security will be out of the public eye , officials say . `` Continue your life as normal . Be vigilant , '' U.S. vice president says .