The Secret Service is enlarging the protective bulwark around the White House complex Wednesday by closing access to the entire fence-line along the mansion's south lawn in the wake of persistent concerns about intrusions.

The new plan, outlined by agency officials, would attempt to replicate a buffer zone created on Pennsylvania Avenue, where iron bicycle racks were placed in front of the perimeter fence to provide officers additional time to react to fence jumpers. That action followed a brazen 2014 breach by a disturbed Iraq War veteran who scaled the north lawn fence and burst through the mansion’s front door.

Under the new proposal, the popular and often-crowded sidewalk bordering the south lawn will be permanently closed to the public beginning at 11 p.m., Wednesday, pushing tourists to the north edge of the 52-acre park known as the Ellipse.

The measures come as the service is confronting a range of security challenges, including increasing encounters with the mentally ill. In the past three years, according to the agency, there have been about 100 incidents in which people have sought to penetrate the 18-acre White House grounds; 95% of those cases have involved suspects with some history of mental illness or emotional disturbance.

Secret Service spokesman Joe Casey characterized the action is part of an "evolving'' strategy to better "mitigate potential threats.'' Contracts for the construction of a taller and more fortified perimeter fence, largely prompted by the 2014 breach, are expected to be awarded later this year.