WASHINGTON — A man carrying a backpack jumped over a fence and was arrested on the White House grounds shortly before midnight Friday, the Secret Service said Saturday, in the first reported intrusion on the lawn in the 51 days since President Trump took office.

A Secret Service official said the intruder was detained at the first layer of security and did not pose a threat to Trump, who was in the residence at the time. The agency, which has not identified the man, said the backpack did not contain hazardous materials.

Security at the White House became a major issue in 2014, when there were several cases in which intruders scaled the fence and entered the grounds. In one episode, a man named Omar J. Gonzalez, carrying a knife, managed to overpower a Secret Service agent inside the North Portico entrance and run through the ceremonial East Room before he was tackled.

The National Capital Planning Commission recently approved plans for the Secret Service to install a stronger and higher perimeter fence around the White House. In 2015, the Secret Service added spikes to the top of the fence on the north and south sides of the White House grounds as a temporary deterrent to jumpers.