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Boston Marathon security: 5,000 police, no drones, backpacks

  • FILE - In this April 20, 2015 file photo, police officers stand watch as Boston Marathon participants race along the course in Boston. Multiple law enforcement agencies will provide security for the 120th Boston Marathon set to be run on Monday, April 18, 2016. (AP Photo/Robert F. Bukaty, File)

    FILE - In this April 20, 2015 file photo, police officers stand watch as Boston Marathon participants race along the course in Boston. Multiple law enforcement agencies will provide security for the 120th Boston Marathon set to be run on Monday, April 18, 2016. (AP Photo/Robert F. Bukaty, File)  (The Associated Press)

  • FILE - In this April 20, 2015 file photo, police officers patrol near the finish line of the Boston Marathon in Boston. Multiple law enforcement agencies will provide security for the 120th Boston Marathon set to be run on Monday, April 18, 2016. (AP Photo/Elise Amendola, File)

    FILE - In this April 20, 2015 file photo, police officers patrol near the finish line of the Boston Marathon in Boston. Multiple law enforcement agencies will provide security for the 120th Boston Marathon set to be run on Monday, April 18, 2016. (AP Photo/Elise Amendola, File)  (The Associated Press)

Three years after two bombs exploded near the finish line of the Boston Marathon, public safety officials have outlined a tight security plan for this year's race.

During a news conference Wednesday, authorities said there will be up to 5,000 law enforcement officers, enhanced security checkpoints and dozens of surveillance cameras along the 26.2-mile route on April 18.

Hank Shaw, special agent in charge of the FBI's Boston division, said officials are unaware of any specific threat against the marathon. He said officials are incorporating lessons learned from attacks in Paris, Brussels and San Bernardino, California, into the marathon security plan.

Officials are asking spectators to leave backpacks and drones at home.

Security has been stepped up significantly since the 2013 bombing killed three people and injured more than 260.