(Updates with parade's conclusion, police comment)
By Daniel Trotta
NEW YORK, Nov 24 (Reuters) - Macy's 90th Thanksgiving Day Parade went off without incident in New York on Thursday amid heightened security, police said, after Islamic State militants abroad encouraged their followers to attack the popular holiday event.
New York police used sand-filled trucks, radiation detectors, bomb-sniffing dogs and heavily armed officers to defend the 2.5-mile (4-km) parade route in Manhattan.
Some 3.5 million people were estimated to attend the annual parade, a nationally televised ritual that initiates the holiday shopping season with giant balloons shaped like cartoon characters.
A New York Police Department spokesman said there were no reports of arrests, injuries or disturbances.
The 82 sand trucks from the Sanitation Department were used to counter a threat by Islamic State, which has called the parade an "excellent target."
The militant group has encouraged readers of its online magazine, Rumiyah, to use motor vehicles to kill and injure people, similar to the way a Tunisian-born assailant killed more than 80 people at a Bastille Day celebration in Nice, France.
The sand trucks weigh 16 tons, and twice that when filled with sand, making them difficult to move even if rammed by large vehicles.
Islamic State, which controls swaths of Iraq and Syria and seeks to inspire attacks by others abroad, claimed responsibility for the July 14 attack in Nice.
"We are aware of some of the reports that have been out there, but I want to assure all New Yorkers there's no credible and specific information of any specific threat directed toward this parade," New York Mayor Bill de Blasio told a news conference on Wednesday.
Police have also used the sand trucks to protect nearby Trump Tower, the home and headquarters of President-elect Donald Trump.
The parade, which began at 9 a.m., ran down Sixth Avenue, one block from Fifth Avenue where Trump Tower is located, and ended at the Macy's department store on 34th Street.
De Blasio estimated 250,000 people came out on Wednesday to watch the giant balloons being inflated.
This year, police banned vehicle traffic from crossing the parade route, unlike in past years when a few cross streets were open. (Reporting by Daniel Trotta in New York; Additional reporting by Curtis Skinner in San Francisco; Editing by Grant McCool and Peter Cooney)