WASHINGTON U.S. authorities are checking whether several people stopped at the Canadian border are linked to an explosion that damaged a military recruiting station in New York, police said on Friday.
"Some pictures of Times Square, including the recruiting station, were found," New York Police Commissioner Ray Kelly told CNN. "So federal officials are going back to take another look and talk to Canadian officials about that stop."
The pre-dawn blast on Thursday, caused by a crude bomb made from low-grade explosives, damaged the recruiting station but caused no injuries. That station, like others, has been the target of protests against the U.S.-led war in Iraq.
Times Square -- known as the "Crossroads of the World" for its shops, restaurants, hotels, theaters and office towers -- was largely deserted when the bomb went off at about 3:45 a.m. EST.
Still, the blast triggered a Pentagon alert for other recruiting stations across the country.
New Yorkers have been on alert since al Qaeda militants slammed hijacked planes into the World Trade Center towers on September 11, 2001, killing more than 2,700 people. The towers were also targeted in 1993 by a truck bomb that killed six people.
Kelly confirmed at least three people were stopped at the Canadian border but he dismissed a possible link between the bombing and a letter sent to some Democratic U.S. congressional offices that referred to the recruiting station.
"The letter is really innocuous," he said, describing it as advice to Democrats on how to win the U.S. presidential election in November.
Kelly said he believed the FBI had concluded that the person who sent the letter was not involved in the explosion.
Authorities are examining surveillance camera footage that shows a person on a bicycle approaching a traffic island, dismounting and walking to the recruiting station. The person leaves shortly before the blast.
Kelly said authorities also were looking into similarities between the recruiting station blast and small explosions at the British and Mexican consulates in 2005 and 2007, both also in the early morning.
(Reporting by Vicki Allen; Editing by John O'Callaghan)