NEW YORK - Heavily armed police were on alert in and around New York City Friday after US officials warned of a 'credible but unconfirmed bomb threat around the 10th anniversary of the 9/11 attacks. In remarks at a security conference in midtown Manhattan, City police commissioner Raymond Kelly cited evidence found in Osama bin Ladens compound in Abbottabad after his death suggesting he hoped to strike on the anniversary. For that reason alone, we need to take precautions as if an actual plot is underway, he said. But the measures were nothing New Yorkers or the well-prepared law enforcement agencies havent seen before, New York City Mayor Michael Bloomberg said Friday. Keep in mind, we have threats all the time, he said on his weekly radio appearance. On the Internet, every day, there are threats of people, particularly around big sporting events and religious holidays, and around commemorations of things like 9/11. And each time the NYPD, with the FBI, we increase our security, which obviously we have done for this. On Friday morning, the mayor rode the subway down to City Hall to help assure commuters the city was prepared. We dont want al-Qaeda or any other organisation to take away the freedoms without firing a shot, he said after getting off the train near the Brooklyn Bridge. Bloomberg urged New Yorkers to just go back to work. And leave it to the professionals. Police staged a show of force at Grand Central Terminal, Pennsylvania Station and the Times Square subway station because of a previously planned counterterror drill with rail agencies. The NYPD formed a zone around the World Trade Centre for a Sunday observance that President Obama and former President George W Bush plan to attend. Along with extra officers the department wont reveal an exact number the security also will include hundreds of surveillance cameras trained on the site, Kelly said. Meanwhile, the United Nations Friday marked the anniversary with a solemn commemoration in the General Assembly Hall, music, poetry and a vow to intensify the battle against terror wherever it is perpetrated in the world. During the ceremony the New York City Symphony orchestra played music and soloists Mzuri Moyo and David DOr respectively sang Still I Rise and Amazing Grace. Inter-faith leaders read a poem by Maya Angelou, after which they lit a candle together, followed by a minute of silence Agencies add: The Department of Homeland Security said Thursday There is specific, credible but unconfirmed threat information, as President Barack Obama ordered boosted counterterrorism efforts. We have taken, and will continue to take all steps necessary to mitigate any threats that arise, the department added in a statement. A White House official confirmed that Obama had directed the counterterrorism community to redouble its efforts in response to this credible but unconfirmed information. Federal officials in Washington, speaking on condition of anonymity, said there was a potential terrorism threat involving bomb-laden vehicles against either the capital or New York. ABC News cited intelligence officials as saying the potential plot involved three individuals who entered the country by air last month with the intention of carrying out a vehicle-borne attack on or around the 9/11 anniversary. It said the plot was hatched by Al-Qaedas leader Ayman al-Zawahiri. Although there was no immediate change to the official US national threat level, New York authorities immediately announced sweeping extra measures, including vehicle checkpoints. A counter-terrorism official said intelligence pointed to possible car bomb attacks and added the threat information came from Pakistans tribal areas. Earlier, US military bases had raised their alert levels, but officials would not say whether this was related to the new threat report. Meanwhile, US Secretary of State Hillary Clinton on Friday said that Al-Qaeda was behind a specific, credible but unconfirmed report of a threat to harm Americans, notably in New York and Washington. We are meeting here in New York ... with the news last night of a specific, credible but unconfirmed report that Al-Qaeda again is seeking to harm Americans and in particular to target New York and Washington, Clinton said in a speech. In a speech ahead of the anniversary, Clinton said it was impossible to foil every plot and that Al-Qaeda was still capable of regional and international attacks. However, she said Washington would wage a relentless campaign against it and, later this month, would set up Global Counter-Terrorism Forum to gather officials to identify threats, devise solutions and share expertise. The group, to be co-chaired by the United States and Turkey, will also include Algeria, Australia, Canada, China, Colombia, Denmark, Egypt, the European Union, France, Germany, India, Indonesia, Italy, Japan, Jordan, Morocco, The Netherlands, New Zealand, Nigeria, Pakistan, Qatar, Russia, Saudi Arabia, South Africa, Spain, Switzerland, the United Arab Emirates and the United Kingdom, the State Department said. Meanwhile, Americas response to 9/11 shows that you dont mess with the United States and that when attacked, we will come and get you, Defence Secretary Leon Panetta said on Friday. Panetta said the hijackers underestimated the country. The people who attacked us on 9/11 were trying to weaken America, trying to hurt America. And instead they strengthened us, Panetta told an audience of police and emergency workers. Because you dont mess with this country, he said. And what we made clear is that when that happens, we will come and get you. Panetta thanked the firefighters and other first responders who rushed to the Pentagon after it was struck by a hijacked airliner on September 11. For 36 exhausting hours, firefighters battled what was truly an epic blaze, he said. Panetta, who took over as Pentagon chief in July, recounted where he was on the day of the attacks ten years ago.