The Secret Service is preparing for the possibility of protests at this weekend’s Army birthday celebration and parade in Washington, D.C., after days of violence in Los Angeles.

“We’re paying attention to what is happening there and we’ll be ready for that if it were to occur here,” the special agent in charge of the Secret Service’s Washington Field Office, Matt McCool, says.

The day-long event is set to mark the 250th anniversary of the U.S. Army, and a military parade is planned for Saturday evening. Hundreds of thousands of visitors are expected in the nation’s capital to attend the events.

The entire celebration is deemed a National Special Security Event because the Department of Homeland Security says it is a potential target for terrorism or other criminal activity.

Mr. McCool says 18 and a half miles of anti-scale fencing is being installed to secure the event. Fencing was already going up around the White House on Monday following the unrest in Los Angeles and elsewhere over the weekend. There will also be 17 miles of other barriers installed. The Secret Service says drones will fly above the area as part of a layered security plan.

The National Park Service says nine groups have requested permits to protest. The small protests will be allowed to take place as long as they remain peaceful, the service says.

The Army has long planned a festival on the National Mall to celebrate its birthday, but the parade was a last-minute edition after President Trump mused about holding one to commemorate his 79th birthday, which falls on the same day. He will observe the parade from the Ellipse in front of the White House.

“It’s such an important moment for this country,” Mr. Trump says. “I think it’s time for us to celebrate a little bit. We’ve had a lot of victories and won two world wars.”

Nearly 7,000 troops from all branches of the military will march down Constitution Avenue, and battle tanks and other large military equipment will be paraded.

Army officials estimate the parade could cost up to $45 million, with an estimated $16 million of that going to repair Washington streets from the expected damage caused by the heavy equipment and tanks. The event will feature dozens of Abrams tanks and Bradley Fighting Vehicles that all weigh more than the streets are equipped to handle.

Air travelers in the region will be affected by the parade as well. Reagan National Airport will close for civilian air traffic for an extended period to accommodate aircraft flyovers and fireworks at the end of the event. The airport says the effects will be significant for fliers, and that getting to the airport will be tough on Saturday evening.