Mayor Bloomberg held a news conference in Times Square just before 9:30 a.m. He said, "The fact that this appears deliberately aimed," at the military recruiting station, "insults every one of our brave uniformed men and women around the world."
The mayor said he wanted people around the country and the world to know that "Times Square is back in business," and that people are again working, shopping and enjoying the city and that "they're not intimidated."
The mayor said the city won't let terrorists threaten their ability to enjoy "the greatest city in the world."
"If it is something that is directed toward American troops, then it's something that's taken very seriously and is pretty unfortunate," he said.
The mayor was joined by NYC Police Commissioner, Ray Kelly and an FBI official. Commissioner Kelly said that the "low-order device" used in the explosion can be purchased in any Army/Navy store.
Kelly also asked anyone with information to call the TIPS hotline: 1-800-577-TIPS.
According to an eyewitness, a man on a bicycle was believed to have thrown the unidentified device at the building, causing minimal damage. The bicyclist, described as wearing all grey and a grey hood, rode away. Several bicyclists were stopped in the nearby area but no arrests were made.
Police were examining numerous security videotapes from the area.
They said investigators would have to examine the evidence to determine exactly what kind of device was used.
Witnesses and tourists staying at the nearby Marriott Marquis reported hearing a loud bang.
Terry Leighton, 49, from London, England, said he was on the 21st floor of the hotel when he heard the blast and looked out a window.
"I thought it could have been thunder," he said. "I looked down and there was a massive plume of smoke. So I knew it was an explosion."
Darla Teck, 25, was on the 44th floor of the hotel. "There was a big bang. I felt it," she said.
Police quickly closed off Times Square to traffic as they investigated.
Subway service was initially halted through the area, and then bypassed the Times Square station. It was restored for the morning commute.
Eyewitness News has learned the improvised explosive is described as a green ammunition can, and pieces of the can were recovered in the shattered gas. There was evidence that a low level explosive was used.
The center is normally staffed by two noncommissioned officers but was empty at the time of the explosion, said Captain Charlie Jaquillard, the commander of army recruiting operations in Manhattan.
The recruiting station is the site of regular anti-war protests, held since the start of the Iraq war in 2003. In October 2005 a group of activists who call themselves the Granny Peace Brigade rallied there against the Iraq war. Eighteen activists, most of them grandmothers with several in their 80s and 90s, were later acquitted of disorderly conduct.
The 520-square-foot station reopened in 1999 after a redesign. It is is decorated with 33-by-14-foot flags rendered in fluorescent lights. The interior contains space for Army, Navy, Air Force and Marine recruiters and one bathroom. It has set national records for enlistment, averaging about 10,000 volunteers a year.
Police said it was too early to say if the blast may have been related to two other recent minor explosions in the city.
On Oct. 26, a person riding a bicycle threw replica grenades loaded with black explosive powder at Mexican Consulate on East 39th Street.
A bicyclist was also spotted near the British Consulate in Midtown just before an explosion rattled that building in the early morning hours of May 5th, 2005.
In both cases, the instruments were fake grenades sometimes sold as novelty items. They were packed with black power and detonated with fuses, but incapable of causing serious harm.
No arrests were made in either of those incidents.