Officials are encouraging Boston Marathon viewers to leave drones and backpacks at home Monday, and to take public transit into the city starting on Saturday to avoid blocked-off streets and traffic snarls.

The security plan for this year’s Marathon will look much like it has for the past two years, with security checkpoints, a heavy police presence, and many cameras. But while terrorist attacks in Europe and California have officials on guard, there is no indication that any group is planning violence here.

“At this time, there is no credible threat to this event, to this city,’’ Boston Mayor Martin J. Walsh said at a press conference Wednesday where city, police, and Marathon officials laid out the security plan for the weekend.

Officials here are sharing information with the FBI and intelligence community both locally and nationally, Walsh said. There will be about 5,000 police officers out on the streets on Marathon Monday, many of them undercover.

Boston Police Commissioner William B. Evans said people should try to swap backpacks, luggage, or large pocketbooks for clear plastic bags to avoid holdups at checkpoints. Drones are completely banned, Evans said, and police are using antidrone technology to monitor them. Transit police will also have a heightened presence, Evans said.

Security was ratcheted up in response to the Marathon bombings in 2013, in which three people were killed and more than 260 injured.

“I was hoping, honestly, that we were going to wean ourselves off that,’’ Evans said. “But I think that what’s happened in San Bernardino and what’s happened in Brussels — obviously this is not the year to scale it back.’’

Road closures will begin Saturday for the Boston Athletic Association 5k and Invitational Mile race, Walsh said. There will be no-stopping restrictions on several streets around the Back Bay in the days leading up to the Marathon, and at about 5 a.m. on Monday, streets around the finish line will begin shutting down, he said.

The US Department of Energy’s National Nuclear Security Administration will conduct low-altitude helicopter flights around Boston to measure naturally occurring background radiation, according to a statement.

Those flyovers will run through Friday. The measurement is to establish a baseline, according to the statement, and is a normal part of security and emergency preparedness.

Evan Allen can be reached at evan.allen@globe.com. Follow her on Twitter @evanmallen.